The scenario is I need to migrate mailboxes from a qmail server to exchange server. I can use imapsync for that. But the issue is after the DNS change (i.e when DNS changed from old qmail server to new exchange server), there could be some mails in source server too.. So I would like to migrate only those new mails which is in old qmail server to new exchange server.

I heard imapsync can be used incrementally but I couldn't get the documents in the web for that.

So how to perform the migration in this scenario and can imapsync be used in this scenario? Or do you suggest any other tool for this?

  • IIRC, imapsync works incrementally by default.
    – Sven
    Apr 4, 2014 at 7:12
  • No, I guess. Because when I tested, it just copied the same migrated emails again making it as duplicate in destination box.
    – FELDAP
    Apr 4, 2014 at 7:54
  • Sounds like a co-existence migration is in your future. Apr 4, 2014 at 13:02
  • Yeah, any advice?
    – FELDAP
    Apr 4, 2014 at 13:43

2 Answers 2


Qmail is a smtp server, not an imap server so the imap server might be something else and knowing what real imap server is used can help to understand issues. You could then fix the title of this question.

imapsync works incrementally by default even when imap server names change, unless a cache is used by options --usecache or --useuid. In that case a part of the cache directory name has to be renamed, with the same change as the names change.

If imapsync generates duplicates by default (without --useuid) then it means it fails to identify messages using its default criteria which are header lines "Message-Id" "Message-ID" and "Received". This default values are ok with Exchange so maybe you use an old imapsync release. To fix this, upgrade imapsync or try:

    imapsync  ... --useheader "Message-Id" --useheader "Message-ID" 

If it fails again, you'd better post to the imapsync mailing-list, we'll fix it there together, and finally post here the solution found.

(I wrote imapsync)

  • Got it working! I was using old version and I got it working after I upgraded to latest version. Now there are no duplicates. Excellent tool! Thank you. :)
    – FELDAP
    Apr 8, 2014 at 10:01

It may be possible -- i think, to just forward mail from one to the other on an address-by-address basis, from qmail to exchange, until your migration is complete. Then make your final changes to DNS.

This may help. http://kmaiti.blogspot.com/2010/05/how-to-configure-alias-forwarder.html

  • I have 500-600 email boxes to be migrated so I think it will be difficult to set the forwarder for each address.
    – FELDAP
    Apr 4, 2014 at 7:03
  • How many are you moving at a time? You can always script out a list of forwarders from boxes that have already moved. Apr 4, 2014 at 14:39

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