Outlook email client signs out customers on iOS and MacOS intermittently

Symptoms

• Customers get signed out of Outlook email clients intermittently only on MacOS and iOS.
• The same happens regardless of the IP address of the customer.
• Plesk uses Dovecot as the mail server.
• The following logs are found in /var/log/maillog at the time of the issue:

CONFIG_TEXT: Aug 27 14:05:07 zeus dovecot: master: Warning: Killed with signal 15 (by pid=383318 uid=0 code=kill)
Aug 27 14:05:07 zeus dovecot: service=imap, user=info@example.com, ip=[203.0.113.2]. Disconnected: Server shutting down. rcvd=119508, sent=147651796

Cause

When Dovecot restarts, it closes all active IMAP connections. This is normal and affects every connected client equally, but only Outlook on macOS and iOS reacts by prompting for the password again, while other clients reconnect silently. This is a client-side session-handling behavior in Outlook, not a server misconfiguration.

Resolution

There is no Plesk-side setting that changes how Outlook re-authenticates after a dropped connection - that logic lives entirely in the email client and does not affect email delivery in any way.

Dovecot restarts could occur for multiple different reasons like system reboots/shutdown, package updates, resource limitations, manual restarts and more. In case the restarts appear too often, look into the reason as to what leads to the restart.

Alternatively. one can configure and use another email client or use the Plesk Webmail for managing the email account.