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I have an OpenSMTPD / Dovecot installation on an OpenBSD server. I recently came across an issue where Dovecot LMTP would reject a message sent to a local user from an address which contains a single apostrophe (e.g. firstname.o'lastname@example.com). Apparently apostrophe, as well as a number of other special characters are valid characters in the local part of the email address (that's everything to the left of the @ character).

The message I get in the logs is: 

Jun 14 11:57:34 atlantic smtpd[42606]: 21749fd12ac76b57 mda delivery evpid=56aed6237d6444a0 from=<firstname.o'lastname@example.com> to=<me@example.org> rcpt=<me@example.org> user=me delay=0s result=PermFail stat=Error ("mail.lmtp: LMTP server error: 501 5.5.4 Invalid FROM: Invalid character in localpart")

where example.com is external domain and example.org is a local one.

The part of the message: LMTP server error: 501 5.5.4 Invalid FROM: Invalid character in localpart is returned by dovecot-lmtp.

My question is: does anyone know of a configuration option, similar to auth_username_chars which lists valid characters in the email address, to stop Dovecot LMTP from rejecting such emails? or maybe you know another way of getting it to accept an email from such address?

My dovecot version is:

$ dovecot --version
2.3.5.1 (7ec6d0ade)

And in case that makes any difference, I'm running OpenBSD 6.5 patched to 005_libssl.

Thanks!

mike
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1 Answers1

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Ignoring the debate on whether an LDA should require any remote address to match the spec, I do believe that the dovecot parser is very close to RFC5322 and what you are seeing is not dovecot LMTP rejecting an address with apostrophe.

You can verify that dovecot is accepting your address by initiating an LMTP session yourself:

$ nc -U /var/dovecot/lmtp
220 example.com Dovecot ready.
LHLO example.com
250-example.com
MAIL FROM:<firstname.o'lastname@example.com>
250 2.1.0 OK
RCPT TO:<postmaster@example.com>
250 2.1.5 OK
DATA
empty
.
354 OK
250 2.0.0 <postmaster@example.com> FOOBAR Saved

If dovecot accepts mail when you manually verify in LMTP, but it fails when receiving from your MTA, you want to scrutinize your mail server configuration.

Is your mail server somehow editing the address before passing it to dovecot? Acquire a transcript of your LMTP session (try lmtp_rawlog_dir in dovecot) and compare if the address is rewritten between SMTP and LMTP. I think the similar limitations that apply to dovecot-lda as opposed to dovecot-lmtp apply when using mail.lmtp, which requires its parameters to be valid command line arguments as well.

anx
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