Emails corrupt and a winmail.dat file attachment added for only one mail box

I'm not sure if this is a Procmail issue but I have one mailbox that's receiving emails from a particular company who use Outlook and all emails sent to that one address are stripped of their proper structure and a winmail.dat file is attached.

This is only happening for single mail box on my server. The rest of our users on the same server receive messages unmodified and intact from the same senders.

We are using Ubuntu 14.04, Virtualmin, Procmail, Postfix and Dovecot combination.

I've tried creating a new mail box on a new server and copied all emails across via an IMAP sync script to the new account but the emails still come through stripped only for that account, others are fine.

I managed to look at samples of the emails sent to our server and compared the source code.

One difference was that after the Received: and before the From: the following line is inserted in the bad email:

Another difference is the email that looks fine has no X-MS-TNEF-Correlator:

And the broken email has:

I've checked /var/log/procmail.log and there's nothing in there that indicates extra filtering. Are there individual settings for a mail box that could be causing this?