Please check Dovecot log /var/log/dovecot/*.log to figure out what happened to the emails.
Thanks ZhangHaungbin
Some errors in /var/log/dovecot/imap.log
Jul 31 15:42:47 mail dovecot: imap(myUser@myDomain.com)<3781><****>: Error: last_login_dict: Failed to write value: dict-server returned failure: sql dict: commit failed: ERROR: duplicate key value violates unique constraint "last_login_pkey"
**UPDATE**[ This error points to database: 'vmail', table: 'last_login'. There was an existing entry the username/domain pair listed above, suggesting the system was trying to add another of the same name. I changed the domain to make a nonsense domain (and will delete), but Question: Under what circumstances will the system try to create a new user/domain, duplicating one that's already there?
Jul 31 15:43:06 mail dovecot: imap(myUser@myDomain.com)<3607><***>: delete: box=INBOX, uid=11, msgid=<***>, size=5659, from=email@from.com, subject=***: Arrival, flags=(\Deleted \Recent)
Jul 31 15:43:06 mail dovecot: imap(myUser@myDomain.com)<3607><***>: expunge: box=INBOX, uid=11, msgid=<***>, size=5659, from=email@from.com, subject=***: Arrival, flags=(\Deleted \Recent)