fsck looping duplicate mdbox GUIDs

[Dirk Koopman]

I have recently updated with 2.2.29.1-avh1~xenial1 ubuntu package on 16.04.

It appears that I have a couple of duplicate GUIDs which fsck can't 
clear so the machine is looping through doing continuous fsck runs.

Any way to determine what the offending messages are and how to delete 
or otherwise stop this?

Jul  1 17:09:24 post dovecot: doveadm(djk at tobit.co.uk): Warning: fscking 
index file /home/imap/djk/storage/dovecot.map.index
Jul  1 17:09:24 post dovecot: doveadm(djk at tobit.co.uk): Error: Fixed 
index file /home/imap/djk/storage/dovecot.map.index: 
log_file_tail_offset 0 -> 24
Jul  1 17:09:24 post dovecot: dsync-local(djk): Warning: fscking index 
file /home/imap/djk/storage/dovecot.map.index
Jul  1 17:09:24 post dovecot: doveadm(djk at tobit.co.uk): Warning: fscking 
index file /home/imap/djk/storage/dovecot.map.index
Jul  1 17:09:25 post dovecot: doveadm(djk at tobit.co.uk): Warning: mdbox 
/home/imap/djk/storage: rebuilding indexes
Jul  1 17:10:15 post dovecot: dsync-local(djk): expunge: box=mup-users, 
uid=1528, msgid=<48707D70.9070108 at optusnet.com.au>, size=3159
Jul  1 17:11:00 post dovecot: doveadm(djk at tobit.co.uk): Error: mdbox 
/home/imap/djk/storage: Duplicate GUID a8e15732b4f91b55414f0000f80b9cab 
in m.385:10102880 (size=860) and m.100:3388046 (size=861)
Jul  1 17:11:11 post dovecot: doveadm(djk at tobit.co.uk): Error: mdbox 
/home/imap/djk/storage: Duplicate GUID 67d2801030161c557a710000f80b9cab 
in m.389:363061 (size=895) and m.169:5349813 (size=896)
Jul  1 17:11:43 post dovecot: doveadm(djk at tobit.co.uk): Warning: 
Transaction log file /home/imap/djk/storage/dovecot.map.index.log was 
locked for 139 seconds (mdbox storage rebuild)
Jul  1 17:11:43 post dovecot: dsync-local(djk): Warning: Locking 
transaction log file /home/imap/djk/storage/dovecot.map.index.log took 
88 seconds (syncing)
Jul  1 17:11:43 post dovecot: doveadm(djk at tobit.co.uk): Warning: fscking 
index file /home/imap/djk/storage/dovecot.map.index

Dirk