Hello all,

I have been using Postfix/Dovecot for some time, but now need to setup Sieve. As I understand this requires Dovecot to do the local mailbox delivery. In my case LMTP would be the best.

Here is the current setup. The users on the system all have local accounts and authenticate with Kerberos via pam_krb5 against kerberos realm domain.tld. They authenticate to the mail server as user@domain.tld. The server name is mail.domain.tld and mailbox names on the mail server are user@mail.domain.tld. User mailboxes are located in /home/user/Maildir.

I went through the configuration described in the documentation (https://doc.dovecot.org/configuration_manual/howto/postfix_dovecot_lmtp/#how...), but hit a weird problem. When LMTP is enabled in Postfix, the delivery fails with an error:

550 5.1.1 user@mail.domain.tld User doesn't exist: user@mail.domain.tld (in reply to RCPT TO command))

If LMTP is not enabled in Postfix, it successfully delivers the messages to ~/Maildir as expected. Can anyone advise me why is this failure with LMTP occurring and how do I fix it?

Thank you, Alex