Troubleshooting email issues for a client. They have multiple email accounts configured in Mail, some of which recently stopped working. I applied the expired security certificate fix and now everything works except their AT&T account. Oddly enough they have a Yahoo email account that DOES work. When I try to modify the non-working AT&T account (via Internet Accounts), it fails to bring up the login window and just gives me this error: "failed to verify the server certificate."
Updating to High Sierra would be the easiest fix, however they need El Cap for compatibility with older software so that option is not on the table.
Updating to High Sierra would be the easiest fix, however they need El Cap for compatibility with older software so that option is not on the table.