[Dovecot] Rebuilding message guid in sdbox

[Renaud Allard]

Hello,

I am running dovecot 2.2.12
Current mail storage is sdbox and I am trying to compress all emails, 
which works fine, except for a few old mailboxes.

If I run the following dsync command
"dsync -u flea -o "mail_plugins=zlib" mirror maildir:~/ndbox"

It fails with:
dsync(flea): Error: Exporting mailbox INBOX failed: Backend doesn't 
support GUIDs, sync with header hashes instead

Doing "doveadm dump flea/dbox/mailboxes/INBOX/dbox-Mails/dovecot.index" 
reveals that there are very old mails (about 5 years ago) without any 
guid like that one:
RECORD: seq=1, uid=1560, flags=0x00
  - ext 1 modseq    :      16043 (ab3e000000000000)
  - ext 3 cache     :        396 (8c010000)
  - cache offset=396 size=20, prev_offset = 0
     - guid:

So, my question is: is there a way to force dovecot to assign a guid to 
those messages?

Best Regards

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