[Dovecot] Some customers receiving duplicate e-mails

[Patrick - South Valley Internet]

Hi all,

I posted this question in the Postfix users mailing list as well - I'm 
not sure if this is Dovecot or Postfix related.

Our old system which we migrated off of was an AIX 5.2 machine running 
most recent Postfix and mbox format with UW-IMAP.  We've migrated to 
most recent Postfix, using Maildir and Dovecot v1.

After we used mb2md to migrate over all our customers, some of our 
customers have called in to let us know they are receiving duplicate 
e-mails.  It's not happening to everyone, it's random (well, I'm sure 
it's not really random, I haven't found the issue yet).

I don't even know where to start.  I looked at the logs, but everything 
looks fine.

How can I troubleshoot something like this?  Have any of you experienced 
the same issue?

Thanks in advance.