I created a new message in Thunderbird, and entered two email addresses in the "To:" bar, separating them with commas. Thunderbird turned these addresses red.
I then clicked on the subject (I did NOT use TAB), and entered something.
I then sent the email. It shows as "Sent", but it never arrived.
Is Thunderbird not properly splitting the comma-separated addresses in the To: line? Is this a known bug?
If you use TAB, Thunderbird visibly fixes the addresses to take two rows.
If you enter a body, Thunderbird doesn't visible fix the addresses, but the message gets delivered anyway.