Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have Postfix and Dovecot running. Postfix is set up to use Dovecot as mail transport. Everything is pretty much by book but every received email is bounced back. I am testing the mail server from gmail.

There are some strange queries for each email:

SELECT email FROM users WHERE email ='receiver@domain' (This is ok)
SELECT email FROM users WHERE email ='receiver@domain' (This is ok)
SELECT email FROM users WHERE email ='' (Why is postfix checking sender's email against db?)
SELECT email FROM users WHERE email ='' (Why is postfix checking senders domain against db?)

First two mysql queries return a valid result (triple checked).

Bounce message: Diagnostic-Code: X-Postfix; unknown user: "" Only useful bit from maillog: status=bounced (unknown user: "")

Any troubleshoot ideas or solutions? I have turned verbose debugging both for Postfix and Dovecot but there is nothing more in the logs.

EDIT: - -

share|improve this question

We should clarify first that how Postfix works has nothing to do with Dovecot. They certainly cooperate but do not depend on each other.

It is a very common thing to check the sender/recipient and the sender domain for validity. This is a basic guard against spam and all sorts of other "evil" activity.

While not uncommon, your postfix is configured to check against a DB. This makes it slightly more difficult to troubleshoot. What is your configuration and Without them any guess will be a good possibility.

share|improve this answer
True, Postfix is configured to check users against the DB. – Lauris Oct 3 '12 at 12:55 - - – Lauris Oct 3 '12 at 12:57

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.