This has been resolved.

well as windows 10 is new to us all. How did you resolve. I have others looking for solution to very similar issues.

andythebeagle said

Another recent issue is Thunderbird not connecting with the server. I don't know if sent mail is going out, but I know I'm receiving anything. My internet connection is working fine for FF or any other browser. I've checked my settings and they seem OK. I've checked default settings in Win10x64 and they are correct. Any ideas??

Well now, yesterday it was fixed by Frontier support. and sometimes repairs are not as they seem. This morning when starting everything up, TB was back to its old tricks. Upon searching for help and getting ready to ask again for help, I found info for setting up my account. Don't know how I missed it yesterday. Wish I didn't find it today.

https://support.mozilla.org/en-US/kb/faq-changing-imap-pop

I followed the directions and now my TB works again. Seems Win10 keeps looking for old configurations of everything, so it reverted back to the problem.

However, upon setting up the pop server a second time, TB and Win10 collaborated to wipe out ''all'' of the local folders associated with my account, and I mean everything. So, caution is the password if you have anything important saved in TB local folders.