I've completely forgot to renew my Lets Encrypt certificate and was greeted with a message:
"Mail can't identify the identity of server mydomain.com". When checking the details I could indeed see that certificate has expired.
I renewed the certificates, but the Mail app still issues the same error message, even though the certificate is now up to date.
What is the least painful way to correct this issue? Since Lets encrypt certificates expire every 90 days, I am going to often get this same error.
I've also deleted the old certificate from Keychain, but the Mail app still issue the same error as if it cached the certificate somewhere.