I like to use digital signing in email, and some friends have done the same and we can exchange fully encrypted email. However, it’s a major issue that iOS has no support for this. If you get an encrypted email, this is all you can see.

Email message dated January 26 2011 at 7:13 PM showing only an unreadable smime.p7m attachment of 9.3 KB due to lack of encryption support.

There is nothing you can do with the email. This is a shame, since it would be really easy to get all this information from my keychain on my Mac.

Hope Apple decides to add support for encrypted email at some point soon.