Stephen Gerke wrote:
Over several months, the Mail connection to the AOL (Verizon) IMAP server fails to connect. The Connection Doctor error message says check the userid & password. The SMTP side works. Eventually it will connect, but will drop out again hours or days later. All of the server URLs, port numbers, userid, password, etc are correct, and have been working for years.
Sounds like an AOL/Verizon issue— I would contact their Support/Help/FAQ/known issues/compatibility /updates
If it is a local issue in the mail app—for problem accounts the go to way to sort things out is to delete the account(s) from the Mail.app, then add it back.
Remove email accounts in Mail on Mac
Remove email accounts in Mail on Mac - Apple Support
Add email accounts in Mail on Mac - Apple Support
Add email accounts in Mail on Mac - Apple Support
Note—
IMAP accounts stay on the server, so no local loss, when you re-sync
POP accounts download and remove from the server—therefor save your inbox/sent box if you want them
“On My Mac" is just that, local folders you created and moved mail into. So no loss