I have several email accounts in Mail, with signatures for each. All are set up in exactly the same way. Account ABC, for some reason, will not accept a signature. Any signature. The sig I created for ABC can be applied to other accounts. Other signatures can go to ABC. But one particular sig cannot go to one particular account. Huh? I even tried deleting the account and setting it up again. Same problem.
OSX Yosemite
Mail 8.2
OSX Yosemite
Mail 8.2