Announcing cyrus-user-map, a local recipient map generator for Postfix

Eric Luyten Eric.Luyten at
Tue Mar 10 06:35:17 EDT 2009

On Tue, March 10, 2009 10:58 am, Farzad FARID wrote:
> Le 10.03.2009 09:59, Stefan Schmidt a écrit :
>> Nice thing, but just out of curiosity, why don't you use postfix'
>> recipient verification mechanism? In smtp_recipient_restrictions add
>> reject_unverified_recipient at a reasonable position in these
>> restrictions. Everything else automagically happens.
> Thanks for asking. In the "Postfix Address Verification Howto"
> ( it says that:
> "/A Postfix MTA verifies a sender or recipient address by probing the
> nearest MTA for that address, without actually delivering mail. The nearest
> MTA could be the Postfix MTA itself, or it could be a remote MTA
> (SMTP interruptus). Probe messages are like normal mail, except that
> they are never delivered, deferred or bounced; probe messages are always
> discarded./"
> This is a very heavyweight process, especially if we have the Cyrus
> database at hand :) So I think that looking up an entry in a hash map is
> much faster and doesn't involve any SMTP/LMTP connection.

Correct, but those probes are pretty lightweight and the results can be
cached by Postfix.
We service dozens of our internal (!) mail domains using those Postfix
probes and performance has never been an issue, even with small mail
backends or small relays.
Recipient address validation is a very useful Postfix feature.

When we started operating IronPort appliances for the main mail domains
we were forced to feed to complete local recipient address list to an
LDAP server, so, yes, your method certainly has its uses and merits.

Eric Luyten, Computing Centre VUB/ULB.

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