We were discussing this in the context of the WMF migration to Phabricator as some people make heavy use of the X-headers for Component/Product from Bugzilla.

It was suggested by a helpful person to use Herald rules.

Herald really isn't quite the right fit.

With the Bugzilla X-headers that are automatically included in all emails, I can do:

• If this email update that was sent to me involves some product, do something (filter it to another folder, add a tag, whatever).

With Herald rules, that becomes:

• If anything happening in Phabricator involves this product, CC me on the email update, and then I can filter based on the Herald rule in the x-header.

Summary: With Bugzilla I can filter the bug mail I'm already getting. With Phabricator I'll have to get way more bug mail. :(

Am I missing something obvious?

In T4973#6, @greggrossmeier wrote:

Am I missing something obvious?

I was!

I assumed "Add me to CC" was the least invasive way of adding the X-Herald-Rules header, but if I selected "Do nothing" it does what I want (the X-Herald-Rules header is set with the rule number AND I only get the email if I'm already subscribed to the task).

(sorry for the spam, I'm over-caffeinated on a Friday afternoon)

Summary: it is possible for people to mimic what eg Bugzilla does but it's double the work (and pointing/clicking work, at that).

Phabricator-world: 1) make a Herald rule and 2) make an email filter rule
Bugzilla-world: 1) make an email filter rule

• We can do this globally, but not until ManiphestTask really implements PhabricatorProjectInterface (T5245).
• These headers aren't (last I knew) actionable in Gmail (since its mail rules can't examine headers). It sounds like there isn't an immediate need for this, but outside of WMF we've seen a lot of Gmail use. We could add a "Projects:" footer by the "To/Cc" footers to deal with this if there's a need for it.

In T4973#17, @epriestley wrote:

• These headers aren't (last I knew) actionable in Gmail (since its mail rules can't examine headers). It sounds like there isn't an immediate need for this, but outside of WMF we've seen a lot of Gmail use. We could add a "Projects:" footer by the "To/Cc" footers to deal with this if there's a need for it.

/me waves as the crazy Mutt user who can do things with random X-headers :)