On 11 Feb 2020 at about 10:00 EST I tried to access my HughesNet email using the Thunderbird app. I received an error message that the mail.hughes.net server had an internal error, I called tech support and was informed that there was no problem with the server and the problem was with my app. I checked two other computers using the same app and came up with the same error message. Iworked for two hours fiddling with Thunderbird and the program started working, Thinking I had somehow fixed the problem I went to other computers to restore email access. Lo and behold these other computers were now able to communicate with the server. There was never anything wrong with the app, there was a problem with the HughesNet server. Tech support was never notified that a problem existed with the server. Do NOT rely on the info tech support supplies. They are only given info from headquarters and apparently never up dated as to server problems. It's always the users computer or app that's the problem.
It can take time for the phone reps to be made aware of issues, especially if they are not widespread.
And though the problem was likely not with your app, please also keep in mind that, though you had problems accessing HughesNet's email through Thunderbird, it doesn't necessarily mean that the problem was with HughesNet. Like the internet service itself, your email access goes through many servers and providers along the way, and the problem could have been with any one of them.