3
3
-------------------------------------------------------------------------------
5
WWAARRNNIINNGG WWAARRNNIINNGG WWAARRNNIINNGG
7
7
The sender/recipient address verification feature described in this document is
8
8
suitable only for low-traffic sites. It performs poorly under high load and may
15
15
a sender (MAIL FROM) or recipient (RCPT TO) address until the address has been
16
16
verified to be deliverable.
18
The technique has obvious uses in order to reject junk mail with an unreplyable
18
The technique has obvious uses to reject junk mail with an unreplyable sender
21
21
The technique may also be useful to block mail for undeliverable recipients,
22
22
for example on a mail relay host that does not have a list of all the valid
47
47
normal mail, except that they are never delivered, deferred or bounced; probe
48
48
messages are always discarded.
50
Postfix Postfix Address
51
Internet -> SMTP <-> verify <-> verification
52
server server database
50
Postfix Postfix Address
51
Internet -> SMTP <-> verify <-> verification
52
server server database
63
63
With Postfix address verification turned on, normal mail will suffer only a
64
64
short delay of up to 6 seconds while an address is being verified for the first
74
74
LLiimmiittaattiioonnss ooff aaddddrreessss vveerriiffiiccaattiioonn
76
* Postfix probes the nearest MTA for the address that is being verified,
77
without actually sending mail to that address. If the nearest MTA accepts
78
the address, then Postfix assumes that the address is deliverable, even
79
when the address will bounce AFTER that MTA accepts it.
76
* When verifying a remote address, Postfix probes the nearest MTA for that
77
address, without actually delivering mail to it. If the nearest MTA accepts
78
the address, then Postfix assumes that the address is deliverable. In
79
reality, mail for a remote address can bounce AFTER the nearest MTA accepts
80
the recipient address.
81
* Sites like AOL may blacklist you when you are probing them too often (a
82
probe is an SMTP session that does not deliver mail), or when you are
83
probing them too often for a non-existent address.
82
* Some sites may blacklist you when you are probing them too often (a probe
83
is an SMTP session that does not deliver mail), or when you are probing
84
them too often for a non-existent address. This is one reason why you
85
should use sender address verification sparingly, if at all, when your site
86
receives lots of email.
85
88
* Normally, address verification probe messages follow the same path as
86
89
regular mail. However, some sites send mail to the Internet via an
added
removed
README_FILES/ADDRESS_VERIFICATION_README
