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PPoossttffiixx SSttaannddaarrdd CCoonnffiigguurraattiioonn EExxaammpplleess
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PPuurrppoossee ooff tthhiiss ddooccuummeenntt
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This document presents a number of typical Postfix configurations. This
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document should be reviewed after you have followed the basic configuration
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steps as described in the BASIC_CONFIGURATION_README document. In particular,
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do not proceed here if you don't already have Postfix working for local mail
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submission and for local mail delivery.
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The first part of this document presents standard configurations that each
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solve one specific problem.
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* Postfix on a stand-alone Internet host
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* Postfix on a null client
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* Postfix on a local network
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* Postfix email firewall/gateway
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The second part of this document presents additional configurations for hosts
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in specific environments.
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* Delivering some but not all accounts locally
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* Running Postfix behind a firewall
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* Configuring Postfix as MX host for a remote site
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* Postfix on a dialup machine
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* Postfix on hosts without a real hostname
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PPoossttffiixx oonn aa ssttaanndd--aalloonnee IInntteerrnneett hhoosstt
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Postfix should work out of the box without change on a stand-alone machine that
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has direct Internet access. At least, that is how Postfix installs when you
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download the Postfix source code via http://www.postfix.org/.
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You can use the command "postconf -n" to find out what settings are overruled
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by your main.cf. Besides a few pathname settings, few parameters should be set
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on a stand-alone box, beyond what is covered in the BASIC_CONFIGURATION_README
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# Optional: send mail as user@domainname instead of user@hostname.
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# Optional: specify NAT/proxy external address.
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#proxy_interfaces = 1.2.3.4
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# Don't relay mail from other hosts.
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mynetworks_style = host
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See also the section "Postfix on hosts without a real hostname" if this is
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applicable to your configuration.
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PPoossttffiixx oonn aa nnuullll cclliieenntt
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A null client is a machine that can only send mail. It receives no mail from
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the network, and it does not deliver any mail locally. A null client typically
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uses POP, IMAP or NFS for mailbox access.
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In this example we assume that the Internet domain name is "example.com" and
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that the machine is named "nullclient.example.com". As usual, the examples show
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only parameters that are not left at their default settings.
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1 /etc/postfix/main.cf:
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2 myorigin = $mydomain
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3 relayhost = $mydomain
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4 inet_interfaces = 127.0.0.1
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5 local_transport = error:local delivery is disabled
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7 /etc/postfix/master.cf:
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8 Comment out the local delivery agent entry
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* Line 2: Send mail as "user@example.com" (instead of
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"user@nullclient.example.com"), so that nothing ever has a reason to send
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mail to "user@nullclient.example.com".
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* Line 3: Forward all mail to the mail server that is responsible for the
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"example.com" domain. This prevents mail from getting stuck on the null
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client if it is turned off while some remote destination is unreachable.
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* Line 4: Do not accept mail from the network.
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* Lines 5-8: Disable local mail delivery. All mail goes to the mail server as
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PPoossttffiixx oonn aa llooccaall nneettwwoorrkk
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This section describes a local area network environment of one main server and
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multiple other systems that send and receive email. As usual we assume that the
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Internet domain name is "example.com". All systems are configured to send mail
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as "user@example.com", and all systems receive mail for
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"user@hostname.example.com". The main server also receives mail for
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"user@example.com". We call this machine by the name of mailhost.example.com.
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A drawback of sending mail as "user@example.com" is that mail for "root" and
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other system accounts is also sent to the central mailhost. See the section
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"Delivering some but not all accounts locally" below for possible solutions.
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As usual, the examples show only parameters that are not left at their default
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First we present the non-mailhost configuration, because it is the simpler one.
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This machine sends mail as "user@example.com" and is final destination for
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"user@hostname.example.com".
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1 /etc/postfix/main.cf:
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2 myorigin = $mydomain
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3 mynetworks = 127.0.0.0/8 10.0.0.0/24
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5 # Optional: forward all non-local mail to mailhost
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6 #relayhost = $mydomain
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* Line 2: Send mail as "user@example.com".
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* Line 3: Specify the trusted networks.
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* Line 4: This host does not relay mail from untrusted networks.
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* Line 6: This is needed if no direct Internet access is available. See also
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below, "Postfix behind a firewall".
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Next we present the mailhost configuration. This machine sends mail as
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"user@example.com" and is final destination for "user@hostname.example.com" as
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well as "user@example.com".
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2 example.com IN MX 10 mailhost.example.com.
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4 /etc/postfix/main.cf:
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5 myorigin = $mydomain
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6 mydestination = $myhostname localhost.$mydomain localhost $mydomain
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7 mynetworks = 127.0.0.0/8 10.0.0.0/24
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9 # Optional: forward all non-local mail to firewall
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10 #relayhost = [firewall.example.com]
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* Line 2: Send mail for the domain "example.com" to the machine
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mailhost.example.com. Remember to specify the "." at the end of the line.
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* Line 5: Send mail as "user@example.com".
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* Line 6: This host is the final mail destination for the "example.com"
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domain, in addition to the names of the machine itself.
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* Line 7: Specify the trusted networks.
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* Line 8: This host does not relay mail from untrusted networks.
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* Line 10: This is needed only when the mailhost has to forward non-local
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mail via a mail server on a firewall. The [] forces Postfix to do no MX
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In an environment like this, users access their mailbox in one or more of the
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* Mailbox access via NFS or equivalent.
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* Mailbox access via POP or IMAP.
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* Mailbox on the user's preferred machine.
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In the latter case, each user has an alias on the mailhost that forwards mail
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to her preferred machine:
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joe: joe@joes.preferred.machine
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jane: jane@janes.preferred.machine
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On some systems the alias database is not in /etc/aliases. To find out the
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location for your system, execute the command "postconf alias_maps".
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Execute the command "newaliases" whenever you change the aliases file.
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PPoossttffiixx eemmaaiill ffiirreewwaallll//ggaatteewwaayy
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The idea is to set up a Postfix email firewall/gateway that forwards mail for
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"example.com" to an inside gateway machine but rejects mail for
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"anything.example.com". There is only one problem: with "relay_domains =
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example.com", the firewall normally also accepts mail for
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"anything.example.com". That would not be right.
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Note: this example requires Postfix version 2.0 and later. To find out what
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Postfix version you have, execute the command "postconf mail_version".
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The solution is presented in multiple parts. This first part gets rid of local
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mail delivery on the firewall, making the firewall harder to break.
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1 /etc/postfix/main.cf:
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2 myorigin = example.com
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4 local_recipient_maps =
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5 local_transport = error:local mail delivery is disabled
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7 /etc/postfix/master.cf:
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8 Comment out the local delivery agent
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* Line 2: Send mail from this machine as "user@example.com", so that no
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reason exists to send mail to "user@firewall.example.com".
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* Lines 3-8: Disable local mail delivery on the firewall machine.
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For the sake of technical correctness the firewall must be able to receive mail
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for postmaster@[firewall ip address]. Reportedly, some things actually expect
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this ability to exist. The second part of the solution therefore adds support
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for postmaster@[firewall ip address], and as a bonus we do abuse@[firewall ip
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address] as well. All the mail to these two accounts is forwarded to an inside
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1 /etc/postfix/main.cf:
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2 virtual_alias_maps = hash:/etc/postfix/virtual
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4 /etc/postfix/virtual:
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5 postmaster postmaster@example.com
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6 abuse abuse@example.com
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* Because mydestination is empty (see the previous example), only address
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literals matching $inet_interfaces or $proxy_interfaces are deemed local.
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So "localpart@[a.d.d.r]" can be matched as simply "localpart" in canonical
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(5) and virtual(5). This avoids the need to specify firewall IP addresses
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into Postfix configuration files.
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The last part of the solution does the email forwarding, which is the real
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purpose of the firewall email function.
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1 /etc/postfix/main.cf:
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2 mynetworks = 127.0.0.0/8 12.34.56.0/24
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3 relay_domains = example.com
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4 parent_domain_matches_subdomains =
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5 debug_peer_list smtpd_access_maps
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6 smtpd_recipient_restrictions =
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7 permit_mynetworks reject_unauth_destination
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9 relay_recipient_maps = hash:/etc/postfix/relay_recipients
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10 transport_maps = hash:/etc/postfix/transport
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12 /etc/postfix/relay_recipients:
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13 user1@example.com x
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14 user2@example.com x
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17 /etc/postfix/transport:
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18 example.com smtp:[inside-gateway.example.com]
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* Lines 1-7: Accept mail from local systems in $mynetworks, and accept mail
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from outside for "user@example.com" but not for
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"user@anything.example.com". The magic is in lines 4-5.
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* Lines 9, 12-14: Define the list of valid addresses in the "example.com"
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domain that can receive mail from the Internet. This prevents the mail
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queue from filling up with undeliverable MAILER-DAEMON messages. If you
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can't maintain a list of valid recipients then you must specify
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"relay_recipient_maps =" (that is, an empty value), or you must specify an
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"@example.com x" wild-card in the relay_recipients table.
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* Lines 10, 17-18: Route mail for "example.com" to the inside gateway
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machine. The [] forces Postfix to do no MX lookup.
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Specify dbm instead of hash if your system uses dbm files instead of db. To
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find out what lookup tables Postfix supports, use the command "postconf -m".
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Execute the command "postmap /etc/postfix/relay_recipients" whenever you change
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the relay_recipients table.
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Execute the command "postmap /etc/postfix/transport" whenever you change the
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DDeelliivveerriinngg ssoommee bbuutt nnoott aallll aaccccoouunnttss llooccaallllyy
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A drawback of sending mail as "user@example.com" (instead of
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"user@hostname.example.com") is that mail for "root" and other system accounts
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is also sent to the central mailhost. In order to deliver such accounts
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locally, you can set up virtual aliases as follows:
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1 /etc/postfix/main.cf:
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2 virtual_alias_maps = hash:/etc/postfix/virtual
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4 /etc/postfix/virtual:
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5 root root@localhost
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* Line 5: As described in the virtual(5) manual page, the bare name "root"
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matches "root@site" when "site" is equal to $myorigin, when "site" is
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listed in $mydestination, or when it matches $inet_interfaces or
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RRuunnnniinngg PPoossttffiixx bbeehhiinndd aa ffiirreewwaallll
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The simplest way to set up Postfix on a host behind a firewalled network is to
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send all mail to a gateway host, and to let that mail host take care of
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internal and external forwarding. Examples of that are shown in the local area
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network section above. A more sophisticated approach is to send only external
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mail to the gateway host, and to send intranet mail directly. That's what
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Note: this example requires Postfix version 2.0 and later. To find out what
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Postfix version you have, execute the command "postconf mail_version".
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The following example presents additional configuration. You need to combine
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this with basic configuration information as discussed the first half of this
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1 /etc/postfix/main.cf:
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2 transport_maps = hash:/etc/postfix/transport
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4 # Optional for a machine that isn't "always on"
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5 #fallback_relay = [gateway.example.com]
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7 /etc/postfix/transport:
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8 # Internal delivery.
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11 # External delivery.
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12 * smtp:[gateway.example.com]
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* Lines 2, 7-12: Request that intranet mail is delivered directly, and that
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external mail is given to a gateway. Obviously, this example assumes that
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the organization uses DNS MX records internally. The [] forces Postfix to
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* Line 3: IMPORTANT: do not specify a relayhost in main.cf.
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* Line 5: This prevents mail from being stuck in the queue when the machine
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is turned off. Postfix tries to deliver mail directly, and gives
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undeliverable mail to a gateway.
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Specify dbm instead of hash if your system uses dbm files instead of db. To
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find out what lookup tables Postfix supports, use the command "postconf -m".
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Execute the command "postmap /etc/postfix/transport" whenever you edit the
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CCoonnffiigguurriinngg PPoossttffiixx aass MMXX hhoosstt ffoorr aa rreemmoottee ssiittee
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This section presents additional configuration. You need to combine this with
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basic configuration information as discussed the first half of this document.
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When your system is SECONDARY MX host for a remote site this is all you need:
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2 the.backed-up.domain.tld IN MX 100 your.machine.tld.
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4 /etc/postfix/main.cf:
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5 relay_domains = . . . the.backed-up.domain.tld
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6 smtpd_recipient_restrictions =
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7 permit_mynetworks reject_unauth_destination
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9 # You must specify your NAT/proxy external address.
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10 #proxy_interfaces = 1.2.3.4
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12 relay_recipient_maps = hash:/etc/postfix/relay_recipients
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14 /etc/postfix/relay_recipients:
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15 user1@the.backed-up.domain.tld x
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16 user2@the.backed-up.domain.tld x
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When your system is PRIMARY MX host for a remote site you need the above, plus:
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18 /etc/postfix/main.cf:
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19 transport_maps = hash:/etc/postfix/transport
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21 /etc/postfix/transport:
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22 the.backed-up.domain.tld relay:[their.mail.host.tld]
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* Do not list the.backed-up.domain.tld in mydestination.
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* Do not list the.backed-up.domain.tld in virtual_alias_domains.
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* Do not list the.backed-up.domain.tld in virtual_mailbox_domains.
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* Lines 1-7: Forward mail from the Internet for "the.backed-up.domain.tld" to
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the primary MX host for that domain.
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* Line 10: This is a must if Postfix receives mail via a NAT relay or proxy
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that presents a different IP address to the world than the local machine.
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* Lines 12-16: Define the list of valid addresses in the "the.backed-
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up.domain.tld" domain. This prevents your mail queue from filling up with
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undeliverable MAILER-DAEMON messages. If you can't maintain a list of valid
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recipients then you must specify "relay_recipient_maps =" (that is, an
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empty value), or you must specify an "@example.com x" wild-card in the
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relay_recipients table.
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* Line 22: The [] forces Postfix to do no MX lookup.
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Specify dbm instead of hash if your system uses dbm files instead of db files.
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To find out what lookup tables Postfix supports, use the command "postconf -m".
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Execute the command "postmap /etc/postfix/transport" whenever you change the
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PPoossttffiixx oonn aa ddiiaalluupp mmaacchhiinnee
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This section applies to dialup connections that are down most of the time. For
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dialup connections that are up 24x7, see the local area network section above.
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This section presents additional configuration. You need to combine this with
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basic configuration information as discussed the first half of this document.
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If you do not have your own hostname (as with dynamic IP addressing) then you
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should also study the section on "Postfix on hosts without a real hostname".
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* Route all outgoing mail to your network provider.
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If your machine is disconnected most of the time, there isn't a lot of
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opportunity for Postfix to deliver mail to hard-to-reach corners of the
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Internet. It's better to give the mail to a machine that is connected all
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the time. In the example below, the [] prevents Postfix from trying to look
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/etc/postfix/main.cf:
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relayhost = [smtprelay.someprovider.com]
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* Disable spontaneous SMTP mail delivery (if using on-demand dialup IP only).
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Normally, Postfix attempts to deliver outbound mail at its convenience. If
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your machine uses on-demand dialup IP, this causes your system to place a
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telephone call whenever you submit new mail, and whenever Postfix retries
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to deliver delayed mail. To prevent such telephone calls from being placed,
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disable spontaneous SMTP mail deliveries.
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/etc/postfix/main.cf:
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defer_transports = smtp (Only for on-demand dialup IP hosts)
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* Disable SMTP client DNS lookups (dialup LAN only).
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/etc/postfix/main.cf:
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disable_dns_lookups = yes (Only for on-demand dialup IP hosts)
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* Flush the mail queue whenever the Internet link is established.
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Put the following command into your PPP or SLIP dialup scripts:
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/usr/sbin/sendmail -q (whenever the Internet link is up)
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The exact location of the sendmail command is system-specific. Use the
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command "postconf sendmail_path" to find out where the Postfix sendmail
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command is located on your machine.
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In order to find out if the mail queue is flushed, use something like:
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# Start mail deliveries.
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/usr/sbin/sendmail -q
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# Allow deliveries to start.
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# Loop until all messages have been tried at least once.
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while mailq | grep '^[^ ]*\*' >/dev/null
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If you have disabled spontaneous SMTP mail delivery, you also need to run
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the "sendmail -q" command every now and then while the dialup link is up,
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so that newly-posted mail is flushed from the queue.
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PPoossttffiixx oonn hhoossttss wwiitthhoouutt aa rreeaall hhoossttnnaammee
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This section is for hosts that don't have an Internet hostname. Typically these
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are systems that get a dynamic IP address via DHCP or via dialup. Postfix will
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let you send and receive mail just fine between accounts on a machine with a
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fantasy name. However, you cannot use a fantasy hostname in your email address
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when sending mail into the Internet, because no-one would be able to reply to
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your mail. In fact, more and more sites refuse mail from non-existent domain
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The perfect solution would be for Postfix to do a mapping from local fantasy
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email addresses to valid Internet addresses when mail leaves the machine
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(similar to Sendmail's generics table). This is planned for the near future.
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In the mean time, the solution with Postfix is to use valid Internet addresses
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where possible, and to let Postfix map valid Internet addresses to local
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fantasy addresses. With this, you can send mail to the Internet and to local
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fantasy addresses, including mail to local fantasy addresses that don't have a
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valid Internet address of their own.
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The following example presents additional configuration. You need to combine
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this with basic configuration information as discussed the first half of this
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1 /etc/postfix/main.cf:
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2 myhostname = hostname.localdomain
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3 mydomain = localdomain
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5 canonical_maps = hash:/etc/postfix/canonical
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7 virtual_alias_maps = hash:/etc/postfix/virtual
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9 /etc/postfix/canonical:
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10 your-login-name your-account@your-isp.com
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12 /etc/postfix/virtual:
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13 your-account@your-isp.com your-login-name
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* Lines 2-3: Substitute your fantasy hostname here. Do not use a domain name
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that is already in use by real organizations on the Internet. See RFC 2606
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for examples of domain names that are guaranteed not to be owned by anyone.
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* Lines 5, 9, 10: This provides the mapping from "your-login-
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name@hostname.localdomain" to "your-account@your-isp.com". This part is
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* Lines 7, 12, 13: Deliver mail for "your-account@your-isp.com" locally,
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instead of sending it to the ISP. This part is not required but is
added
removed
README_FILES/STANDARD_CONFIGURATION_README
