I had in my archive namespace[1] an INBOX folder and did not really get why it was there so I deleted it. Now this command generates map index error (doveadm force-resync does not fix it ;))
[@ ~]# doveadm -o namespace/4archives/location=mdbox_deleted:/home/mail- archive/testtest/mdbox/Archive -o mail_location=mdbox_deleted:/home/mail- archive/testtest/mdbox/Archive:INDEX=/home/archiveindex/testtest/index mailbox status -u testtest 'messages vsize' 'INBOX'
doveadm(testtest): Error: mdbox map /home/archiveindex/testtest/index/storage/dovecot.map.index corrupted: Unexpectedly lost INBOX uid=1 map_uid=4726 doveadm(testtest): Error: Mailbox INBOX: Failed to lookup mailbox status: mdbox map /home/archiveindex/testtest/index/storage/dovecot.map.index corrupted: Unexpectedly lost INBOX uid=1 map_uid=4726
doveadm purge -u testtest
fixed this