Fmail now email supports standard RFC-5322 email message ID

FMail the free native Mac application for Fastmail users., now enables users to get the RFC-5322 compliant ID of the selected email. This can be used by Hook. Hook Pro users can update their scripts using the information on FMail’s Hook page. We’ll build it into Hook soon.

That way fmail users can email their colleagues hook://email/ links to emails, and they can open them with any email app that uses the standard. Similarly, fmail users will be able to receive and open hook://email/ links received from, Airmail, etc. users.

If you switch to the new scheme, using hook:///email URLs, however, when you invoke Hook on a previously hooked email message in fmail, you will not see the old hooks. (The script could be modified to write the old URL to a file or something.)