Plesk Premium Email in Plesk shows the warning: Preferred domain redirects are not supported and will break various features

Symptoms

Plesk Premium Email in Plesk shows the warning:

PLESK_WARN: Preferred domain redirects are not supported and will break various features.

Cause

Preferred domain redirects (e.g. from example.com to www.example.com) are currently not supported and will break various features.

Note: It includes Seafile, Mattermost, ActiveSync, and Collabora integration.

Resolution

1. Log in to Plesk
2. Go to Domains > example.com > Hosting Settings
3. Switch Preferred Domain to None
4. Click the OK button