Can't send hotmail from iMac but can from iPhone

I have a hotmail.co.uk account which I have been using for years to send and receive mail from both my iMac and my iPhone. Recently, I have been unable to send from my iMac but receiving mail to iMac and sending and receiving from iPhone work fine.

When I look under Connection Doctor on the iMac for the STMP for that account i get the message...Could not connect to this SMTP server, check your network connection and that you entered the correct information in the Account preferences. Also verify that the server supports SSL. If it does not, deselect the "Use TLS/SSL" checkbox in the Server Settings tab of the Account preferences.

As I have made no changes to account preferences or anything else whilst using this account for years, I cannot see why it should suddenly stop sending.

I have discovered that if I enter Account and change the host name from stmp.live.com to stmp-mail.outlook.com and re-enter my password, I can then make the connection and send mail.

Each time I turn the iMac back on, I have to change the host name and re-enter the password again in order to be able to send mail.

I have three questions that I would love your help on please:-

Why has this problem started to happen ?

Am I doing any damage by changing the host name etc as mentioned above ?

Is there a way that I can make whatever change is required and NOT have to redo it every time I turn the iMac on ?

Any guidance would be much appreciated.

Thank you,

Vicki