all you see in Thunderbird for digitally signed mail is an icon in the mail header. an envelope with a red spot on it. No attachment. Same with most mail clients that understand s/mime. Usually only those that don't understand s/mime show the attachment because they don't know what it is.

hmm normally atleast in outlook it clearly shows you have a s/mime certificate.

I checked in both OWA and Outlook after sending a mail to my self from TB --> nothing showed.

If i chose to encrypt i can still read it on my mobile that doesn't have s/mime support (didn't enable the extra plugin for android there), if i do the same with my outlook s/mime it: 1) becomes unreadable after encryption on devices that do not support s/mime 2) shows a certificate icon

So in all accounts i am pretty sure my TB doesn't do anything with s/mime. I actually seen similar complaints in the original addon before it was integrated in TB it self.

Regards, Marco

lets experiment... my email address is in my profile (click on my ugly mug) send me a signed mail. and I will reply encrypted is the signing worked from you.

I have send you an email with digitally sign checked. thank you for your support and quick answers so far, it's really appreciated :-)