Attachments getting corrupted

[mrbusy]

I have a bizzare problem with email. My configuration is as follows:

Email is directed to a single ISP POP3 account which accepts anything@mydomain.com. The contents of the POP3 account are preiodically downloaded by a POP3 to SMTP application and forwarded on to be virus scanned. From the virus scanning server email is directed on to and Exchange 2000 server where it is delivered to the appropriate person.
This has worked fine for some months, but yesterday and today email attachments have started being corrupted for no apparent reason. Outbound email goes direct from the E2K server via SMTP and is not affected.
Im made suspicious by the fact that I have not made any changes to our config in months but our ISP apparently "upgraded" their email server last week.
The attachments which are affected are not of any one file type and are of average size (we think) before being damaged. The email still shows an attachment but what is left is a corrupt file of around 64-66 bytes in size. Emails affected are coming from different senders at various times of the day to different recipients.
Has anyone ever seen this kind of thing happening before? Any thoughts gratefully received.

 

[sioxley]

Its not renaming the attachments with a *.DAT extension is it?

 

[mrbusy]

No. The attachments appear to be normal until you try and open them and then you get a message saying the file is corrupt. When you look at the properties all the files have retained their name and file type but are only 64 bytes in size.