lda: Warning: Failed to parse return-path header: Invalid character in localpart

[Christian Authmann]

Hello,

Sometimes, when delivering mails, this warning appears in my syslog:

 > lda(...): Warning: Failed to parse return-path header: Invalid 
character in localpart

dovecot-lda still exits with 0 and the mail is inserted into my inbox.


Looking at the mails in question, I determined that the error is caused 
by a multiline Return-Path header. Here's a testcase:

--- snip ---
Return-Path:
   <nowhere at example.com>
From: "Nowhere" <nowhere at example.com>
To: redacted at example.com
Subject: Testcase for lda warnings
Date: Wed, 31 Jan 2018 12:00:00 +0000

This is a message body.
--- snap ---

Copy into a file, with \r\n line endings, then run something like this:
 > cat testcase.txt | /usr/lib/dovecot/dovecot-lda -e -d '<username>'
with a username recognized by your running dovecot installation.

The header is 'Return-Path:', \r\n, two spaces, '<...>', \r\n

According to rfc2822 folding rules, that should be valid - the 
Return-Path header allows CFWS at that location.


The error message originates in lib-lda/mail-deliver.c in 
mail_deliver_get_return_address(), while the invalid character message 
seems to originate from one of several places in lib-lda/mail-deliver.c


Ciao,
Christian Authmann