I've been having problems with emails sent through two addresses using different servers set up on Thunderbird not arriving with their sender email address. This is only happening since upgrade to Thunderbird 38. I have reinstalled 37 and everything is fine, upgraded again using "Help" "About Thunderbird" and the problem recurs. I haven't tried installing 38 directly from a download. It doesn't happen when I send using GMail through Thunderbird, presumably GMail's systems insert the correct information.