Cannot add new SMTP server for outgoing mail

I have MB Air with Sonoma 14.4.1 . I migrated data from my older Mac to this new one. I am having problems with SMTP server setup for one of my email accounts (I have alltogether 2 email accounts). The new settings do not save and always revert to its original values.

I conatcted my email provider and they advised to remove the concerned email account and add it again. First I removed just the email server, however I was not able to add a new email server.

Therefore, I completely removed the account from my email and also made sure that the account is removed from internet accounts (System setup -> Internet accounts). Restarted the computer.

I added the removed account again as a new account, however it does not set the outgoing mail server as per entered data. It just assigns no outgoing mail server to the account.

I am still unable to add any new outgoing mail server at all.

Pls help and advice how to add a new outgoing email server..

Thanks.