How do I program mail I send to go into a specific folder?

Well, it's not going to work well with sent Mail, but Mail>Preferences>Rules...

Use rules to manage your email inbox in Mail on Mac - Apple Support

A better idea would be virtual Mailboxes, called Smart Mailboxes...

Use Smart Mailboxes to organize emails in Mail on Mac - Apple Support

collettagraphix Said:

"How do I program mail I send to go into a specific folder?: Is there a way to write a script to put sent mail in a particular folder?"

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Use Apple Developer Forums:

Putting a post in the Apple Developer Forums, you may get a more direct answer in there: Apple Developer Forums. If you put a post in there, reply back with the URL of it, for reference.

https://gist.github.com/Zettt/6551639

https://superuser.com/questions/416593/shortcut-for-moving-an-email-to-another-folder-in-mail-app

Need AppleScript to move email to another… - Apple Community