Migrating *just* Mail to a New MBP-M1 (Big Sur)

Thanks, Sberman. I knew that would be the ideal, but it would take me months to find enough time to clean up the various emails at the various servers with their assorted webmail interfaces. The ISP for my primary addresses only displays a number of emails at a time on which you can act and it is very slow (unrelated to our internet speed). So, was trying to avoid that approach (acknowledging that I should have been taking care of that all along (for 20+ yrs)). In the interim (since I posted) this is what I came up with:

1) In the morning on day X I will turn all mail accounts on my old MBP off.

2) I will set up the various accounts on my new MBP and create a new rule for it to filter all emails received before day X directly into the trash.

3) When the downloads are through (I'll go do some yard work), I'll empty that trash and leave the accounts active.

4) I'll then go back to the old MBP and gather my mail from there and port it into the new Mail program.

What say the Community of the feasibility of this approach?

BTW, if anyone knows of a URL describing how to ensure one copies all their mail files on the old Mac to drop in the new one, I'd appreciate it. Would hate to mess that portion up.

Thanks!

Follow Up: This approach actually accomplished my objective. As previously mentioned - the ideal approach would be to have cleaned this up on the mail server - this would have taken *many* hours (>50K messages, and a poor webmail interface). This took maybe 1/2 hour. Once the new MBP was through downloading all the referenced mails from the server, I selected and deleted it all. Then I imported all the exported mailboxes from my old MBP (including the 'Sent' mailboxes for each account). The new MBP now contains only the emails I wished to transfer and any new email going forward. I also copied the Mail Preferences so that the Rules transferred as well. (I realize I can delete email from the server with Mail client settings and probably need to come up with a plan to do so going forward).

Cheers!