What catnipman wrote in reply 23.
Preserve (back up) old e-mail messages.
Do everything to clear out old e-mail application installation.
In general, failures to receive / send (if not network issues) are sticky parts of credentials (certificates, keys, username-and-password-combos stored in the Microsoft Windows OS [and other] catacombs).
You probably will be able to use both a newer Outlook and latest Mozilla Thunderbird.
And you may have to piece together the restoration of the old e-mail messages that you saved and/or magically recover from whatever “cloud,” Hotmail, and Outlook servers have that data.
I suppose I can uninstall, and reinstall, Thunderbird, and that might fix the problem?
But there's the other issue. I never receive MS's verification codes, whether sent by text or email. I went to their website, and learned this was an issue for some people, but there were no helpful solutions.