[MlMt] Help extending Message View headers

[Tariq Magdon-Ismail]

Hi,

I was looking to extend the message view headers to also include the source mailbox and came across this post from 2012:

[[MlMt] Let the Mail-preview show particular header-parts] https://www.mail-archive.com/mailmate@lists.freron.com/msg00339.html

I tried the suggestions in the thread, adding the customization to "~/Library/Application Support/MailMate/Resources/Layouts/headersFormatting.plist" but could not get it to work. Just to make sure I wasn't messing things up I copied another example from Benny posted here:
[[MlMt] Customizing Headers Display] https://www.mail-archive.com/mailmate@lists.freron.com/msg00633.html
I used the posted example verbatim, but that didn't have any effect.

Additionally, as a test, I also copied "/Applications/MailMate.app/Contents/Resources/Layouts/headersFormatting.plist" and changed "From:" to "FooBar:" but, again, that made no difference either.

(N.B.: In all cases I did a syntax check with plutil and restated MM).

What am I missing? The posts I dug up are quite old, so is there something that has changed? Is there a setting to enable low level customizations (though I couldn't find any mention of such here: https://manual.mailmate-app.com/customization)?

Regards,
-Tariq

P.S. When is shortFormatting vs longFormatting applied?