How will Mail handle an SMTP server port number change? Our email provider is making a change soon to our SMTP servers, changing the port number to 587 and blocking ports 25 and 465.

Our clients who use Apple Mail have the "Automatically manage connection settings" box ticked, which hides the usual Port &amp; TLS / SSL &amp; Authentication options.

I am assuming that having that box ticked will handle this change by detecting the port numbers that don't work, then trying the other common port numbers, but I'm not sure if it is safer to disable it &amp; add in the settings manually.

Does anyone have any information about how Mail will handle a change like this, if the automatic option is set?
There might be two things that you have to do:

It should work automatically without any intervention after the port upgrade. But to make it smooth, you might need to re-add your account in Apple Mail. 

You can manually modify and add specified port too but it depends upon your email provider. However, in most cases, it should go automatically.