Encrypted email attachment showing smime.p7m

[cgeez]

I sent encrypted email with an attachment (2M) from Outlook 2007 on my PC. Then I accessed email account on iPad and the attachment shows smime.p7m and will not decrypt. Encrypted email with attachments of smaller size can be decrypted fine on the iPad, as well as, text can be read fine. iOS is version 5.1.1. I can access and read all the emails (smaller/larger) fine in Outlook on my PC. How come I can read the smaller encrypted email attachments on the iPad, but cannot read the larger encrypted email attachments on the iPad?

Thanks.