I was attempting to fix a Thunderbird issue and came upon this page...
This page is very outdated and badly needs fixing. It's not even certain that the settings shown here are still all correct.
Thunderbird is up to version 60.x. Here are some of the issues;
a. How to find the account settings is changed. It's now on Options/Account settings from a menu item ifn the upper right corner
b. How to add an account has changed
c. The incoming server settings are now under 'Server Settings'
d. The outgoing server settings is no labeled 'Outgoing Server'