Issue Postfix - warning: connect to transport private/plesk-domain.org.uk-123.145.167.189-: Connection refused

[MHC_1]

Server operating system version

Alma Linux 9

Plesk version and microupdate number

Obsidian 18.0.6

We have the following mail log details:

/var/log/mail.log

Jun 9 10:02:05 serverName postfix/smtpd[2253641]: connect from host86-178-175-114.range86-178.btcentralplus.com[86.178.175.114]

Jun 9 10:02:06 serverName postfix/smtpd[2253641]: 22BBB52000093: client=host86-178-175-114.range86-178.btcentralplus.com[86.178.175.114], sasl_method=CRAM-MD5, sasl_username=[email protected]

Jun 9 10:02:06 serverName psa-pc-remote[2253076]: 22BBB52000093: from=<[email protected]> to=<[email protected]>

Jun 9 10:02:06 serverName postfix/cleanup[2253834]: 22BBB52000093: message-id=<[email protected]>

Jun 9 10:02:08 serverName amavis[2245222]: (2245222-07) Passed CLEAN {AcceptedOutbound}, AM.PDP-SOCK/SUBMISSION LOCAL [86.178.175.114] [86.178.175.114] <[email protected]> -> <[email protected]>, Queue-ID: 22BBB52000093, Message-ID: <[email protected]>, mail_id: oWVRfxJQCDlT, Hits: -0.875, size: 4604, 2075 ms

Jun 9 10:02:08 serverName psa-pc-remote[2253076]: 22BBB52000093: py-limit-out: stderr: INFO:__main__:Setting 'X-PPP-Vhost' header to 'domain.org.uk'

Jun 9 10:02:08 serverName psa-pc-remote[2253076]: 22BBB52000093: py-limit-out: stderr: PASS

Jun 9 10:02:08 serverName psa-pc-remote[2253076]: 22BBB52000093: spf: stderr: PASS

Jun 9 10:02:08 serverName psa-pc-remote[2253076]: 22BBB52000093: check-quota: stderr: SKIP

Jun 9 10:02:08 serverName psa-pc-remote[2253076]: 22BBB52000093: dk_sign: stderr: PASS

Jun 9 10:02:08 serverName postfix/qmgr[2252799]: 22BBB52000093: from=<[email protected]>, size=4577, nrcpt=1 (queue active)

Jun 9 10:02:08 serverName postfix/qmgr[2252799]: warning: connect to transport private/plesk-domain.org.uk-123.145.167.189-: Connection refused

Jun 9 10:02:08 serverName postfix/error[2267273]: 22BBB52000093: to=<[email protected]>, relay=none, delay=2.4, delays=2.4/0/0/0, dsn=4.3.0, status=deferred (mail transport unavailable)

Jun 9 10:02:09 serverName dovecot[2253344]: service=imap, user=[email protected], ip=[86.178.175.114]. Disconnected: Logged out rcvd=4737, sent=119008

Jun 9 10:02:09 serverName dovecot[2253344]: imap-login: Login: user=<[email protected]>, method=CRAM-MD5, rip=86.178.175.114, lip=123.145.167.189, mpid=2269172, TLS, session=<I3VHrCA3qcpWsq9y>

Note: 123.145.167.189 is the server IP.
The core detail here is:

Jun 9 10:02:08 serverName postfix/qmgr[2252799]: warning: connect to transport private/plesk-domain.org.uk-123.145.167.189-: Connection refused

BUT:
Other domains on the server are sending and receiving OK. This domain (multiple addresses on this domain) has an issue.

Due to this I am wary of doing the Plesk Repair on the main.cf or Master.cf files.

How can we find out what the specific issue is?

Everything was working fine until a couple days ago. The email address now has 30 mails queued all with the above issue.

 

[Kaspar]

Perhaps this support article helps to narrow down the issue:

https://support.plesk.com/hc/en-us/articles/12377953797783-Unable-to-send-email-in-Plesk-mail-transport-unavailable

 

[MHC_1]

Perhaps this support article helps to narrow down the issue:

https://support.plesk.com/hc/en-us/articles/12377953797783-Unable-to-send-email-in-Plesk-mail-transport-unavailable

Yes I have already read and used this documentation. All parts of the settings are as set in the documentation.

As stated - it seems to be only one domain that is at issue.

How do we debug and resolve where the issue is coming from?