Hey ecoalex2. Long time no see.
Though I can't help with the current problem you're seeing, as I don't use Thunderbird and don't know much about 3rd party apps for email, I'd think about migrating to another email provider, or at least starting an account with one to have it as an alternative when the time comes. Maybe one of the more prominent free services, like Gmail, Outlook or Yahoo Mail. With ISP provided email progressively going by the wayside, it's very likely that this will happen with HughesNet's at some point as well. And though I don't know this for sure, I think they may have already stopped offering email to new sign ups.
I think it's a combination of fewer people using ISP provided email and the free email by the aforementioned providers tending to be more complete and up to date with today's technology and abilities. I'm kind of lucky in that I've been using Outlook and its prior versions for my primary email for nearly 25 years, having first gotten an account when I got dial-up service from MSN in the late 90s. Were it not for the HN Community notifications, which I forward to my MSN email anyway, I'd never use my HughesNet email.
Just something to think about. I hope you're able to get the problem resolved quickly.