When Outlook runs into issues, whether on the web or its desktop version, you can fix them and get back to your mail.
But Outlook is the default mail client. I've checked this in a number of places: in Outlook itself, in the Internet Options control panel thing, in the Set Program Access and Defaults program, and the ...
Microsoft is investigating several issues causing email synchronization and connection problems when using the classic Outlook desktop client. The first bug causes "Can't connect to the server" errors ...