How can I see if an e-mail is signed in "Mail" (using an Exchange account)? Usually, a signed message shows a checkmark icon. Clicking on this icon displays the certificate that was used to sign the message:



Not so when a message lies in an exchange mailbox, and is displayed with "Mail" on MacOS (tested up to 10.10):



The iPad, on the other hand, handles the exact same message just fine. It is also connected via Exchange protocol to the server:



So: How can I enable this also on "Mail" on OS X? Or is this a bug, or even a permanent restriction?
It was most likely a bug. I had the same behaviour and after the latest update (10.10.2) Mail is showing the information again.



Edit

As commented by user2216335 the Security information is not always shown.

Apple Mail was able to recognise the signature from my example:

Content-Type: application/pkcs7-signature; name=smime.p7s;
smime-type=signed-data Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature


but not from a message sent by Apple Mail

Content-Disposition: attachment; filename="smime.p7s"
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64