I've set up my iPhone 3GS with iOS 5.1 to send digitally signed emails. And the initial tests by sending emails to myself worked, where I would see the "checkmark" next to the sender's (my) name.
However, sometimes signed emails I send to myself (again as a test) behaves different. Instead of the checkmark, I get an attachment that called smime.p7s. This happens when I view that email in desktop clients as well (such as Thunderbird).
Can anyone help me troubleshoot this issue?