P.S. using TB 115 on Linux Ubuntu 20.04

I sent a message to a mailing list from a gmail IMAP account, entering the gmail address in the To: box and the list in the Bcc: box. The message was received by all recipients and the gmail account, and was copied to the gmail Sent Mail account. Are you doing it differently?

Not exactly. Here is an example:

I press C-n or select "New Message" from the account of myemailaddress@gmail.com TB opens a "Write" window with myemailaddress@gmail.com as the "From" field and I type in with completion "mLEmacs <Help-gnu-emacs@gnu.org>" I write something and hit "Send" and the email (OP) is sent.

When I check for a new message there is no copy downloaded of the email that I just sent. With my previous email address, I would have almost immediately gotten a copy of the OP.

The response above is consistent with every listserv and google group that I have use for decades. With non-gmail addresses.

With the gmail address I do not get a copy of the OP, no do I get copies of subsequent replies I might send to that thread. This is very inconvenient as it makes the thread harder to follow.

Thanks for the reply. I hope I have been clearer. My email address has been obfuscated, of course. Quotation marks around text are illustrative and not literal.

First, this is not an act by Thunderbird. My guess is Google senses that, since you sent the message, you don't need a copy. Listservs and Google Groups may be doing that.