2022 - For all those that just started having problems. Outlook changed their POP and SMTP servers (without really notifying users). Go to Account Settings > E-mail > highlight your account (msn/outlook/live/hotmail) > Change tab > Change Account popup > change the following settings to . . .

Incoming mail server: pop-mail.outlook.com
Outgoing mail server (SMTP): smtp-mail.outlook.com

If you're still receiving incoming email, then you may not have to change incoming setting for now, yet, will most likely have to in future, so might as well do it now.

Unfortunately it took me 4 days and 12 different tries (ports, authentications, security, firewall, anti-virus changes) to finally find that they had just changed their servers.