Apple Mail won’t connect to SMTPserver

Hi!

I have an M1 Macbook Pro running Tahoe. Apple Mail just suddenly stopped connecting a day or so ago to the SMTP server where I have two mail accounts. Other accounts (mostly gmail) are fine. I also have Outlook on the same machine and it has the same problem. I deleted the problem accounts from Mail and tried to re-install them - but that has not worked - I still can’t connect. I have the right credentials as I am still able to access the accounts on my iPhone and Windows PC. Tried to re-install the accounts in safe mode and no change, so not an antivirus issue.

Grateful for any ideas on where to turn. Thinking I need to delete and re-install Apple mail altogether….. :-(