Latest Thunderbird Release
Since the latest Thunderbird release I've noticed the client has really slowed, especially when sending email. I used to be able to click Send and a few seconds later my email, including attachments, was sent. Now I sit and wait for up to a minute while the T-bird spinner spins and then eventually sends the email. Even the smallest email with no attachments takes longer.
I understand you want to continue to make Thunderbird better. I've been a programmer for 30 years myself. But I also understand that just because you can do a thing with software doesn't always mean you should do it. To the best of my knowledge the email server I use has not changed. So I put the blame on Thunderbird.
Email clients are supposed to send and receive email, period. Trying to turn Thunderbird into a one-stop shop is not a good idea. There are many of us out here who don't use Outlook specifically for that reason. You had a great client up until this last release. See if you can get it back.
Ndryshuar