SMTP settings keep changing

Every now and then one of the settings under SMTP keeps changing, and my emails fail to send.
When I look it has selected ‘Force usage of SSL/TLS’
If I change this to ‘Use SSL/TLS if available’ then my emails are sent okay.
I click on ‘Save & Close’, but then the next day the same thing happens, and when I look it has changed back to ‘Force usage of SSL/TLS’ again, and I have to change it again.
I found one answer in the forums suggesting changing to change port to 993 and select ‘use SSL/TLS on special port’, but that didn’t work.
Why can’t it just keep the settings that I have selected?
Can you please help?

The security policies are specific to the ports.

Make sure you are using one of these combinations, and it should not change:

Port 587 = Force usage of SSL/TLS
Port 25 = Use SSL/TLS if available
Port 465 = Use SSL/TLS on special port (legacy)

993 is for IMAP, not SMTP that is why it wouldn’t work.

That can be caused by your anti-virus/firewall application. After you have the correct settings as above, disable your anti-virus completely, and see if the send works.

I choose port 25 and ‘Use SSL/TLS if available’ and it works. I click on ‘Save and Close’.
The problem is that later on it changes by itself back to ‘Force usage of SSL/TLS’ and stops working.
So I have to change it again.

As it keeps changing to ‘Force usage of SSL/TLS’ I have changed the port to 587. Works at the moment, so I will see how it goes.
Many thanks for the reply.

Who is the email provider?

Sky are the email provider