In most email clients a small 'preview text' is shown which contains whatever text it can extract from the start of the message. Because of all the boiler plate which is typically in most moodle emails, eg forum, this ends up being just clutter in the preview instead of something meaningful which would enable a reader to get a better sense of what is in the email before opening it.

There is a slightly hacky way to give email clients some targeted preview text which is independent of the actual html visible text when yo open it:

https://customer.io/docs/custom-preheader-text

https://litmus.com/blog/the-ultimate-guide-to-preview-text-support

https://litmus.com/blog/the-little-known-preview-text-hack-you-may-want-to-use-in-every-email

I'm proposing to:

1) support this in the message api for emails via the 'smallmessage' field

2) then optimizing the contents of that field for certain emails eg forum

The semantics of 'smallmessage' are very poorly defined, so it would be good to tighten that up a little in the docs as part of this. For instance the whole event data already has metadata for who the message from from or to etc so I think the smallmessage should be defined as not including any boilerplate which includes these, and if you want it for a particular message output then it can reconstruct it from the various pieces of metadata it has, rather than every message provider inconsistently deciding what it's smallmessage should include or not.