Thanks a lot. Your suggestion "mutt -f sent" works, but I was looking for a solution to get out of a running mutt session (where I read emails) straight into the sent folder.
Your links didn't help. No references to sent folder.
But ... after digging (for quite some time), I found this here:
This works exactly as desired!
I can change from a running mutt session to the sent file and back!
Thanks for your kicks.