Overview
After upgrading to Plesk Obsidian v18.0.76, the Dovecot mail server may experience repeated crashes when processing IMAP requests involving message movement or deletion. This issue is associated with a specific assertion failure in the Sieve plugin storage component.
Symptoms
The system logs will display the following panic error:
Feb 19 11:59:29 plesk01 dovecot: service=imap, user=redacted@redacted.tld, ip=[1.2.3.4]. Panic: file imap-sieve-storage.c: line 216 (imap_sieve_add_mailbox_event): assertion failed: (ismt->src_box == NULL || ismt->src_box == src_box)Cause
This behavior is caused by a known defect in dovecot-pigeonhole v2.4.2, which was included with Plesk 18.0.76. The issue occurs when certain IMAP clients (including mobile applications and desktop clients such as Thunderbird) move or delete messages while the Sieve plugin is active. A conflict arises during the internal handling of the source mailbox reference, triggering an assertion failure. This defect has been documented in both the Dovecot community archives and Plesk support forums.
Resolution
The issue has been permanently resolved in Plesk Obsidian 18.0.76 Update 2. Applying the latest update is strongly recommended. If updating is not immediately feasible, apply the following configuration workaround to disable the problematic attachment detection option:
- Create a new Dovecot configuration file by executing the following command:
// apply the fix echo 'mail_attachment_detection_options =' > /etc/dovecot/conf.d/999_fix_crash.conf - Restart the Dovecot service to apply the changes:
// restart dovecot systemctl restart dovecot
Troubleshooting & Verification
- Verify that the Dovecot service is running without errors by executing: systemctl status dovecot.
- Monitor /var/log/maillog for any recurring panic messages after applying the workaround.
- If crashes persist, ensure no conflicting configuration files exist in /etc/dovecot/conf.d/ and schedule an upgrade to Plesk 18.0.76 Update 2 or later at the earliest opportunity.
