After upgrading to Yosemite, Apple Mail no longer recognizes my S/MIME certificate. This was working in Mavericks. I've checked Keychain and the certificate is valid, even evaluated it as S/MIME for my email address and it passed. However, emails I send do not contain the certificate and I cannot figure out any way in Apple Mail to sign them.
I've read Apple's help article and it says an icon should display next to the From: field on new emails. However, I only use a single account with Apple Mail, so the From: field doesn't display. If I do add another account, just so that field displays, no signing icon is shown when I create a new email.
Any help would be greatly appreciated.