Error 'Cannot send message using the server san.rr.com' on Mac

Is it an IMAP account?

This may still work...

I actually managed to sort it out! Rather than set up as google I clicked other… added my gmail address and used the app password that I’d managed to suss out and generate ( rather than my gmail password!) and it worked!! 

Go through setting everything up to a Fake Server, none of the Apple choices, replace the part after the @ sign with like @fakeserver.net when setting up this fake account, use all the right ports authentication, & passwords, wait for mail to say it failed do you want to save this account anyway, say yes, then you can go back in & edit the 2 servers to Earthlink.com or whatever instead of @fakeserver.net

Apple mail will not let me add a GMail ac… - Apple Community

Hey Barbara Selby!

Good question! Either some setting isn’t configured as it should be, or there is a software or even email provider conflict, it depends.

Was it working fine not too long ago? Then suddenly stopped working? If so were there any changes made in between? (A move, a change in Internet or email provider, any account change, etc.).

I do recall with Monterey two distinct issues in particular with Spectrum Internet and their Road Runner email service not working on Macs while other accounts work fine, or the account works fine on a non-spectrum network.

Another question which me help clarify the situation is…..Do you have other email accounts in Apple Mail? And if so, do they send just fine? And finally if you can send email from the same account on another network, (Even using your phone’s hotspot if available)?

I can think of a dozen possibilities of a cause, but more info will definitely help!

In my experience, most of the time this issue can be resolved by removing and re-adding the account in System Preferences > Internet Accounts, of course you’d need to know the account email and password, and sometimes the server settings. Thanks! Glad to help if I can as anyone here! BDAqua had an interesting fix I’ve never seen before, but now am interested to try if I ever have to come across this again)!

You may not even have to use the @fakeserver part, perhaps just routing around Apple's auto setup by using "Other".

👍