MAC MAIL (smtp server - offline)

This is to address smtp server going offline:

troubleshooting steps:
Option 1.

* Mailbox - Take account Online

if that doesn't work...

Option 2.

* check smtp server
* Mail - Preferences - Accounts - Outgoing Mail Server (SMTP)
* remove current smtp server ➖ then add again ➕
* take account offline then online
* quit and reopen Mac Mail


Option 3.

* delete and recreate account


Anyone experiencing the same problem? I have att.net. One email working with same smtp server. Other email setup, same att account with the same settings but smtp offline. Is this a Mac update issue? Time warner email accounts having the same problem.