You just add the new address as a new account. This doesn't affect your address book and all your stored contact data.

The bad news is that if you have been using an account provided by windstream and you're now switching to one provided by twc, you have to advise all your existing Contacts of your new address, because when the old account closes, they won't be able to email you on your old address.

Do you not have your own domain and associated email address for your business? No account with someone such as google that is independent of your ISP?

What's your motivation for changing ISP now? I wonder if you have fully considered the possible disruption to your business?

It is the 1st time in 20 years that I have a choice. My website forwards through windstream into Thunderbird. Is there a way to migrate everything to a new account? I'm leaving Windstream, but am not locked in to any one new.

Your windstream.net account will in all likelihood cease working when you finish your relationship with windstream. Regardless of which email client you use, if the account stops working then messages addressed to it will not and can not get to you.

If you change your email address, you have to tell all your email correspondents to use your new address. Or you have to arrange with windstream to keep the account working so it can forward to a new account. That would almost certainly cost you money. It may well be cheaper to stay with windstream than pay both them and twc.

Or just resign yourself to switching to a new account. This time get yourself one which isn't tied to any particular ISP. Look at gmail, aol, outlook.com, gmx.com etc. Or better, buy a domain to use with your business. It looks far more professional.

But if you use an account offered by twc, then you will at some point in the future have exactly the same problem all over again.

Thanks for the replies. Guess I screwed up before I knew it was a problem.