Plesk/Postfix Forwarders: Some mail does not get forwarded
Symptom:
Emails are not forwarded and postmaster receives messages like:
Subject: Postfix SMTP server: errors from unknown[xxx.xxx.xxx.xxx]
Transcript of session follows.
Out: 220 {mail server} ESMTP Postfix
In: EHLO {senders address}
Out: 250-{mail server}
Out: 250-PIPELINING
Out: 250-SIZE 10240000
Out: 250-VRFY
Out: 250-ETRN
Out: 250-STARTTLS
Out: 250-AUTH DIGEST-MD5 PLAIN LOGIN CRAM-MD5
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250 DSN
In: MAIL FROM: <{senders email}>
Out: 250 2.1.0 Ok
In: RCPT TO: <{recipient address}>
Out: 250 2.1.5 Ok
In: DATA
Out: 354 End data with <CR><LF>.<CR><LF>
Out: 451 4.3.0 Error: queue file write error
In: QUIT
Out: 221 2.0.0 ByeCause:
If you create a mail account without a mailbox and only a forwarder, it seems unnecessary to create a password for the account. Sadly this is not the case!
Solution:
Set a password for the account under Plesk > Domain > {domain} > Mail Accounts > {mail account} > Preferences
