I do not know if it is Thunderbird or the fact that there are basically no email servers left out there that actually send them. The Failure delivery notifications that were coming to people who had they email address used by spammers resulted in the whole new term of backscatter. these days to prevent having your server put on a blocklist you basically have to disable DSN s recipients like yahoo, Hotmail etc consider the DSN floods to be spam.

Thanks for your reply, Matt!

You might want to file a bug for the failure however. If you think it is Thunderbird that is at fault. https://bugzilla.mozilla.org/

Thanks again, Matt. The more I think about it, I believe it is an issue with my service provider. When I used to receive the delivery status notification, the return email address was from the service provider.

I'm going to call their tech support again and try to get to the bottom of this.