What is your problem in the first place?

Mediacom say's thunderbird has blocked port 25 and they have to unblock it

This is rubbish. Thunderbird does not block any port. You'll need to provide more details about your problem.

Do you maybe use a firewall program that blocks that port?

Also, is it this company, Mediacom Cable: https://mediacomcable.com/site/about.html

If so, their help page doesn't mention using port 25 at all: https://support.mediacomcable.com/content/what-are-pop3-and-imap-mail-server-settings-mediacom