madasa,

You are not ignorant by asking questions…
certainly not here at the Forum. I am glad to help.

The Avast boot scan should not ask you to change ISP.
I do not suspect that Avast is the program asking.

Are you using a proxy server of any kind as part of your email client?

Avast might ask you to change POP/IMAP/SMTP server address, but not ISP.

Please explain exactly what you were doing when the error message appeared; the exact error message; and then…
Right click on the A ball in the tray and open up the Log Viewer.
Click on each icon in the left side panel and let me know if any alert messages are shown in the main panel and the category it appeared in.

I will take it from there…