Emails sent from a MAC client

I have been having issues with emails beig sent via a MAc client to Lotus Notes. We have Win XP Pro installed on all our computers. I use Mail Marshal as an email content scanner for external emails and the emails seem to appear fine in Mail Marshal. As soon as the email is snet to Lotus Notes, either the attachments or the content of the email disappears. We get a couple of emails from people using MAC clients. Have tried to find some info on this issue, but have had no luck.