I use Mailwasher and Outlook on a Vista PC and receive from one sender duplicate mails. All other mails from other senders are single. I have emailed the sender and requested they check their end. I receive an auto reply (in duplicate) that they are looking into it. They then mail with the reply that they have checked their system and tested for this and found no problem. They suggest it is my Outlook that may be at fault.
The Mailwasher shows a single mail when run and it is when I open Outlook, a receive pulls two identicle copies of the mail. The inbox then shows (2)unopened mails.
If mailwasher find mail from other senders, that mail is also received but only single copies of their mail arrives in the inbox.
I also have an XP machine with Mailwasher and Outlook and to complicate things this only receives single mails from the same sender. It does seem to point to the Vista machine having a problem.