How do I prevent postfix from adding this Reply-To header twice?

3x5

6/19/24, 11:18 PM

I am running a mail server with Postfix, and I have set this line in /etc/postfix/header_checks.pcre:

/^To: [email protected]/  PREPEND Reply-To: [email protected]

[email protected] is a forwarding address. If someone sends an email to [email protected], it'll forward to a number of other addresses. However, I want the Reply-To line to be [email protected], so all replies go to everyone.

My line works, but the problem is that it's adding the 'Reply-To' header twice. I suspect the mail server is receiving the message, prepending the line, then sending out emails to each of the recipients, adding the line again. I have tried this:

if /^To: [email protected]/
!/^Reply-To: [email protected]/  PREPEND Reply-To: [email protected]
endif

The logic here is 'if this is going to [email protected], and the Reply-To header is not [email protected], then prepend the Reply-To header. The problem is, this still doesn't work. It adds the Reply-To header twice.

My understanding is that postfix header_checks can't determine whether a header is present or not, only what the content of it is. I am at a loss as to how to get this header going in only once.

100

1 + 0

postfix

smtp-headers

Score:0

Server

3x5

7/11/24, 8:36 PM

OK, I do have a working solution for this now. In /etc/postfix/main.cf, make sure you have this line:

header_checks = pcre:/etc/postfix/header_checks.pcre

Note that this starts with header_checks and not smtp_header_checks. Then, inside this file:

/^To:.*board@example\.org/ PREPEND Reply-To: <[email protected]>
/^(Reply-To:.*)board@example\.org/ IGNORE

So there it is. If the email is going to a specific address, add the Reply-To header. Also, if the Reply-To header is already what you want, do nothing.

I don't know why it works this way, despite there being no nested condition and despite the order seeming to be incorrect, but after trying quite a lot of options, this one is working for me, consistently. I hope this helps you too.

+ 1

3x5

7/17/24, 2:02 PM

Sorry, I had what I thought was a solution, but it was buggy so I removed it. I just posted the fixed, correct solution.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: How do I prevent postfix from adding this Reply-To header twice?

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