Mail not downloading

Who is the eMail provider?

See if it's like this...

Mac's Mail App is not as modern as iOS's Mail app, Many eMail providers now require a separate App Password different from your eMail password…

Then you may need Ways to securely access AOL Mail…

https://help.aol.com/articles/allow-apps-that-use-less-secure-sign-in

Or it may just need an App Password separate from the gMail password…

https://support.google.com/mail/answer/185833?hl=en-GB

https://discussions.apple.com/thread/253943442?answerId=257410962022#257410962022

Note from PrestoWebDesign…

Trying to add Gmail account to Apple Mail… - Apple Community

Trying to add Gmail account to Apple Mail… - Apple Community

Yahoo has gone to this too...

https://help.yahoo.com/kb/access-yahoo-mail-third-party-apps-sln15241.html

Yahoo App password…

Generate and manage third-party app passwords

Some older, third-party email apps (that do not use our Yahoo branded sign in page) require you to enter a single password for login credentials. To access your Yahoo Mail account on these apps, you'll need to generate and use an app password. An app password is a long, randomly generated code that gives a non-Yahoo app permission to access your Yahoo account. You’ll only need to provide this code once to sign in to your third-party email app.

https://help.yahoo.com/kb/access-yahoo-mail-third-party-apps-sln15241.html

Using app passwords with apps that don't support two-step verification (microsoft.com)

What about application passwords? Will that keep working?

If application passwords are being used for MFA (Multi Factor Authentication) along with basic auth as another auth mechanism, then when basic authentication is disabled, app passwords used for MFA will stop working too.

Where can I find more information?

There are several resources that we wanted to provide here as additional reading:

• Basic Authentication Deprecation in Exchange Online – September 2022 Update – this is a comprehensive post containing more information about this effort.
• Deprecation of Basic authentication in Exchange Online – our official documentation related to this effort, with links to much more information and guidance.

https://techcommunity.microsoft.com/t5/exchange-team-blog/exchange-online-email-applications-stopped-signing-in-or-keep/ba-p/3641943

Exchange Online email applications stopped signing in, or keep asking for passwords? Start here. - Microsoft Community Hub

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

To find out if it's system wide or user specific, try this...

Open System Preferences>Users & Groups, unlock the lock, click on the little plus icon, make a new admin account, log out & into the new account.

Does it work in the new account?