qmail dropping outbound messages with attachments?

[dvdpa]

Hi

I have a customer who uses a mac base machine and he is reporting that when he sends out mail to some clients that have attachments such as word docs or zip files they never reach the destination.

Three separate people have reported it to him from unrelated companies. I had him email a test message to my yahoo account and I did get all the messages and attachments. I know some large corporations will strip out some attachments but not drop the entire email. Could qmail be doing this?

Plesk 8.1.1 RHAT ES 4 4PSA spamguardian and cleanserver

Thanks

Chuck