Plesk Premium Email in Plesk shows the warning:
Preferred domain redirects are not supported and will break various features.
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.
- Log in to Plesk
- Go to Domains > example.com > Hosting Settings
- Switch Preferred Domain to None
- Click the OK button