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:

  CONFIG_TEXT: INTERNAL ERROR
  Could not load message from server

  CONFIG_TEXT: 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.