Emails migrated from cPanel are not visible in Plesk webmail.

Symptoms

• Emails were migrated from cPanel
• There is a storage directory inside Maildir of the email account at /var/qmail/mailnames/example.com/mail/Maildir
• Email messages files have the following format ../m.xxx where xxx is some number

Cause

Migrated emails from cPanel are in mdbox format which is yet to be implemented in Plesk.

Resolution

1. Convert email format to maildir in CPanel as explained in the documentation:
   https://docs.cpanel.net/whm/email/mailbox-conversion/

2. Log into Plesk

3. Re-sync migration from Tools & Settings > Migration & Transfer Manager > 203.0.113.2 > List of subscriptions and click the Re-sync button beside example.com

Additional Information:

How to migrate only mail content to Plesk server using Plesk migrator?
How to migrate domain web / mail / database?
UserVoice: Dovecot: mdbox and alternate storage support: Vote for this feature, most voted features are likely to be implemented in a future Plesk releases