Our goal is to have a copy of any email sent by a specific SMTP user account bcc'd to another email address.

With Postfix, we can setup an outgoing email address to always BCC another address on messages that are sent.

This can be done with a line in main.cf:

sender_bcc_maps = hash:/etc/postfix/sender_bcc 

And then in /etc/postfix/sender_bcc:

[email protected] [email protected]

But if the user simply changes thier outgoing mail settings to send mail as [email protected], the BCC breaks. What the user can't change, however, is their SMTP username.

So we really need a way to setup Postfix to create a BCC when a message is sent by an SMTP user logged in as user, regardless of what email address that person claims to have.

Is this possible? How?

  • Why do you even allow users to send from other email addresses?
    – sebix
    Aug 20, 2017 at 8:14

1 Answer 1


You may use reject_sender_login_mismatch to force match between smtp auth and envelope sender address. It may deliver solution acceptable for most situations.

  • I agree that this would be the correct answer. Please explain this a little, though. Aug 20, 2017 at 7:21
  • It looks like there may be some additional setup required for this, since it relies on an SMTP username to email lookup table, smtpd_sender_login_maps. I wonder if there is a way to check if the user part of the email addresses matches the SMTP username without a lookup table (or with a regular expression)?
    – Nick
    Aug 21, 2017 at 10:58

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