Output raw mail for use with other tools

[Reisen]

Is your feature request related to a problem? Please describe.
Pop seems to be limited at the moment to sending mail via SMTP or Resend, but access to the raw mail body would make this tool much more useful for working with other tools. For example:

• Opens up use other delivery agents, for example I use msmtp with many accounts so I can more easily manage the various mail servers I have to use (Gmail at work, Personal Gmail from home, Protonmail, etc):
  pop -o - | msmtp -a gmail
• Pipe the output to mdeliver from the mblaze toolkit for managing file based delivery targets; especially useful if you have an sshfs mounted maildir from another system for example:
  pop -o - | mdeliver /mnt/sshfs/some-host/mail/INBOX
• Pipe the output through other command line tools to modify mail before sending, I.E sed
pop -o - | anonymize.sh | tee /tmp/mail.txt | msmtp -a gmail

Basically right now pop is a beautiful UI for creating mail, but does not fit well into the command-line philosophy of being a combine-able tool with the rest of the mail ecosystem.

Describe the solution you'd like
A flag for simply outputting the raw resulting mail body/headers without processing. I.E: pop -o -

Describe alternatives you've considered
Setting up a local MTA that can be targeted by SMTP and scripting that would work but it is a lot of overhead.