For what it’s worth other CRMs (for eg ActionKit, Salsa, BSD) automatically include an ID like this or a cookie on every email link, so the staff at the organization do not need to remember to include it manually.

Providing some mechanism like this would be a neat improvement as it would allow us to build seamless external experiences. We already have most of the server side code written to support the other CRMs I mentioned.

Yes, that was what I was asking.