The steps described at the above link don't work at all. That was the first thing I checked. It seems to be for me iOS does't send out the signature correctly. I'm using my gmail account as Exchange mailbox configured on the iPad and turned on Smime and signature. The cert and the chain installed correctly. If I send out a mail with the same certificate to another exchange mailbox with Outlook 2010 on my notebook, it's fine. If I send it out from the iPad, Outlook desn't recognize it, just shows the attachment like any client which dosn't support Smime. Something is really wrong here. :-(
I've made some other tests:
1. Gmail account configured as Exchange mailbox on the iPad (the only reason for this config is to able to sync contacts as well)
2. Certificate installed, SMIME and digital signature turned on
3. Sending out a digitally signed mail to exchange recipient
4. Recipient client (Outlook 2010) cannot recognize the mail as a signed message, an attachment appears with name smime.p7s
5. Sending out digitally signed mail and read it on an iOS device
6. Same behavior as in point 4.
7. Configuring gmail account as Gmail mailbox on iPad (no option to sync contacts)
8. Turn SMIME and Sign on at the above mailbox on iPad
9. Send out a digitally signed mail to iOS and Outlook 2010 clients.
10. Everything is fine, the mail recognized as a signed message on both type of clients
This seems to be a bug with SMIME support on iOS 5.x.x when configuring gmail account as Exchange mailbox. Does anyone know how to address this to Apple to fix?