More precisely, what purpose does moving Mark to BCC, and then acknowledging that and addressing him in the letter, serve? Why not just exclude him from the conversation completely, or leave in CC if you're still addressing him?
You say thanks to Mark, but save him countless minutes of pressing Delete on the future CC's back and forth. Busy people get already too much e-mails and it is often a pain to get out from those discussions.
Another instance where it is useful is when asking a question at a mail list but asking that anyone who answers only addresses the you not the whole email list.
Just send the email with the list in BCC, and that's gonna be automatic.
From: me
To: me
Bcc: foo-enthusiasts
Subject: [survey] what's your favorite version?
What's your favorite version of foo? Write me off-list
and I'll post back to summarize.
Imagine the maillist of all your coworkers and you want to let them know you are selling a few items. It's not rude to force responses to be only to you. This reduces the amount of email everyone gets.
More precisely, what purpose does moving Mark to BCC, and then acknowledging that and addressing him in the letter, serve? Why not just exclude him from the conversation completely, or leave in CC if you're still addressing him?