I am using Thunderbird on 2 computers, ver. 16.0.2 and 38.6.0 and both window 8 and 10, both quit sending emails 3 days ago. by not sending I mean they appear to be sent, a copy goes to sent file but, a none are received by anyone, including test to myself. I Spent over 7 hrs. with the isp, Windstream, trying to fix this as it appears the problem may be on their end. In the end I am informed that Windstream will no longer accept emails sent from any Thunderbird platform. I asked why they are doing this and they informed me it was because so many people are using Thunderbird? What? I have no reason to doubt this statement as both quite suddenly. I am trying to pursue this issue with Windstream but, I am basically getting nowhere. For now I am forced to use Windtream's sorry excuse for an email program.

Can they do this and is there a way to fix this?