Are you receiving any error messages? ".gov" servers often have more restrictions on email services

Hi David, thank you for your response and attention to this matter. No error messages were received. I found out that my e-mails were not being received, when I felt it odd that the recipients did not provide any replies out of courtesy, which they usually do, and I called them by phone. I presume that there is no fix and that the shortcoming is inherent to the .gov server receive side. As I mentioned, I can receive messages from the .gov server via Thunderbird. But, I thought I'd go ahead and present this shortcoming to the Thunderbird forum, in case, there might be a fix on the Thunderbird side.

Thank you.

You might try changing sig if present, omit attachments, see if your anivirus is attaching an ad (such as AVG or Avast), and see if your domain is on any blacklists. Yes, these are hard to fix, as I've been down that road as well.