Issue Mail forwarded on the server in the target mailbox is delivered to the SPAM folder

[W4ru]

Server operating system version

Ubuntu 24.04.1 LTS

Plesk version and microupdate number

Plesk Obsidian 18.0.67

Introduction:
I frequently use a mailbox with several alias names and then sometimes have it forwarded to a mail address of another domain on the same Plesk server.
I also use this permanently for other domains. So far everything has been fine.

Now I register a circumstance: Messages from the Plesk forum, which are delivered to [email protected] ( an alias to [email protected] ) are also forwarded to [email protected] in the mail setup.
In the roundcube of [email protected] (no rules in Roundcube, sive entry in the mail directory does not exist) the notification is delivered by Plesk in SPAM.

Here is the log, which shows the process in detail:

2025-01-22 15:30:04    postfix/qmgr    removed
2025-01-22 15:30:04    postfix/pipe    to=<[email protected]>, relay=plesk_virtual, delay=0.89, delays=0.81/0/0/0.08, dsn=2.0.0, status=sent (delivered via plesk_virtual service)
2025-01-22 15:30:04    postfix-local    dmarc: stderr: STOP
2025-01-22 15:30:04    dovecot            service=lda, [email protected], ip=[]. sieve: msgid=<[email protected]>: stored mail into mailbox 'INBOX.Spam'
2025-01-22 15:30:04    dmarc            DMARC: smtpdomain=plesk.com maildomain=plesk.com [email protected] stamp=1737556204 ip=unknown adkim=strict aspf=relaxed p=QUARANTINE sp=UNSPECIFIED pct=100 align_dkim=fail align_spf=fail spfres=unknown dkimres=pass dmarccheck=DMARC_POLICY_QUARANTINE dmarcstatus=DEFER
2025-01-22 15:30:04    dmarc            SPF record was not found in Authentication-Results
2025-01-22 15:30:04    postfix-local    dk_check: stderr: PASS
2025-01-22 15:30:04    postfix-local    from=<[email protected]>, to=<[email protected]>, dirname=/var/qmail/mailnames
2025-01-22 15:30:04    postfix/qmgr    from=<[email protected]>, size=12943, nrcpt=1 (queue active)
2025-01-22 15:30:04    amavis            (1152109-25) Passed CLEAN {AcceptedInternal}, AM.PDP-SOCK/MYNETS LOCAL [127.0.0.1] [195.214.233.100] /AM.PDP <[email protected]> -> <[email protected]>, (ESMTPS://195.214.233.100), Queue-ID: 43F1A8582B, Message-ID: <[email protected]>, mail_id: AFaInvvlUzve, b: g2wRz-sz4, Hits: -, size: 13000, Subject: "Question - Wanted: Best practice for certificates (Lets Encrypt) two separate Plesk servers for www ", From: <[email protected]>, helo=localhost, [email protected], dkim_sd=default:domain1.tld, 746 ms
2025-01-22 15:30:03    postfix/qmgr    removed
2025-01-22 15:30:03    postfix/pipe    to=<[email protected]>, orig_to=<[email protected]>, relay=plesk_virtual, delay=1.2, delays=0.6/0/0/0.57, dsn=2.0.0, status=sent (delivered via plesk_virtual service)
2025-01-22 15:30:03    postfix/cleanup    message-id=<[email protected]>
2025-01-22 15:30:03    postfix/pickup    uid=30 from=<[email protected]>
2025-01-22 15:30:03    postfix-local    send message: id=S1165069 from=<[email protected]> to=<[email protected]>
2025-01-22 15:30:03    dovecot            service=lda, [email protected], ip=[]. sieve: msgid=<[email protected]>: stored mail into mailbox 'INBOX'
2025-01-22 15:30:03    postfix-local    arc-sign: stderr: PASS
2025-01-22 15:30:02    postfix-local    dmarc: stderr: PASS
2025-01-22 15:30:02    postfix-local    dk_check: stderr: PASS
2025-01-22 15:30:02    dk_check        DKIM Feed: No signature
2025-01-22 15:30:02    postfix-local    from=<[email protected]>, to=<[email protected]>, dirname=/var/qmail/mailnames
2025-01-22 15:30:02    postfix/qmgr    from=<[email protected]>, size=10213, nrcpt=1 (queue active)
2025-01-22 15:30:02    psa-pc-remote    check-quota: stderr: SKIP
2025-01-22 15:30:02    psa-pc-remote    spf: stderr: PASS
2025-01-22 15:30:02    psa-pc-remote    py-limit-out: stderr: SKIP
2025-01-22 15:30:02    psa-pc-remote    py-limit-out: stderr: INFO:__main__:No SMTP AUTH and not running in sendmail context (incoming or unrestricted outgoing mail). SKIP message.
2025-01-22 15:30:02    amavis            (1152108-25) Passed CLEAN {AcceptedInbound}, AM.PDP-SOCK [195.214.233.100] [195.214.233.100] /AM.PDP <[email protected]> -> <[email protected]>, (195.214.233.100), Queue-ID: 4326E8581A, Message-ID: <[email protected]>, mail_id: qAPhY1F9CEaa, b: g2wRz-sz4, Hits: -, size: 10196, Subject: "Question - Wanted: Best practice for certificates (Lets Encrypt) two separate Plesk servers for www ", From: <[email protected]>, helo=ch.origin.talk.plesk.com, 73 ms
2025-01-22 15:30:02    postfix/cleanup    message-id=<[email protected]>
2025-01-22 15:30:02    psa-pc-remote    grey: stderr: SKIP
2025-01-22 15:30:02    grey            Remote host ch.origin.talk.plesk.com in white list
2025-01-22 15:30:02    psa-pc-remote    from=<[email protected]> to=<[email protected]>
2025-01-22 15:30:02    postfix/smtpd    client=ch.origin.talk.plesk.com[195.214.233.100]

As you can see, the message sent to plesk@ is " stored mail into mailbox 'INBOX' " while the forwarded copy is " stored mail into mailbox 'INBOX.Spam' "

Hints of the current thread here: Question - Incoming mail is stored in Junk folder I have checked all of them, there are no sive settings. The config files under /etc/dovecot/conf.d show me no anomalies.
Warden is running on the server. For other accounts there is no SPAM sorting if it is not causal based on the score.