If it`s any help this problem also occurs with some attachments sent out with e-mails from ntlworld.com to some other ISP recipients.
A number of us on various different ISPs recently received an e-mail sent with an attachment by one of our number who is with ntlworld.com. Some of us received the attachment but for others it was stripped somewhere en-route. We all checked it was not our security removing it by passing it from others who received it complete to those who didn`t and there was no problem other than for those sent from ntlworld.com accounts. We have no idea of the cause and have decided it is one of the great mysteries of the internet.
To overcome the problem we now avoid attachments as much as possible and include all text in the body of the message. Where they are absolutely necessary attachments are forwarded through known, `good` routes. Painful but it works.