Unable to verify digital signature-How do I get rid of this?

I get message in my Apple mail SENT box for every email I send for one specific gmail address-

The digital signature for this message is incorrect. The message may have been tampered with or corrupted since being signed by 

This seems to be some kind of glitch that happened, when I was trying to create a verified signature in an Adobe PDF document, using Keychain. Everyone receiving mail from this specific address now gets a warning that the email cannot be verified as coming from me. I want to get rid of this altogether, and not have any signature verification for this email account. In the Apple Keychain app on my iMac, I can see a certificate present that matches the certificate that displays with all outbound email from the account in question. If I delete that certificate in Keychain, will that solve the problem and make this issue clear away? Or it will make things worse, or disable the account on my iMac? My name is mis-spelled in the certificate ( I am sure that my fault, a typo), so maybe that is the cause of the problem. But there seems to be no way to edit the certificate in Keychain (tried that). So if I can just delete the certificate, will I be problem solved? OS is Mojave 10.14.6-I am not able to upgrade at this time because of third-party driver availability issues.