Unable to open emails for specific mailbox on Plesk with Courier IMAP/POP3 server: Could not load message from server

Symptoms

• Unable to read mail in Roundcube/Hord for a specific mailbox with Courier IMAP/POP3 server:

  external ERROR
  Could not load message from server

  SERVER ERROR
  Could not load messages from server

Cause

Corrupted courierimapuiddb file.

Resolution

1. Connect to the server via SSH

2. Recreate courierimapuiddb file by moving and restarting services.

   # mv /var/qmail/mailnames/example.com/johndoe/Maildir/courierimapuiddb /var/qmail/mailnames/example.com/johndoe/Maildir/courierimapuiddb.bak
   # service courier-imapd restart && service courier-imaps restart

Note: if a mail client like Outlook is used for this mailbox it will force it to re-download all messages.