[kragen]

i feel like if we're talking about a header the user isn't aware of, most users probably won't be able to use it to unsubscribe either

[stubish]

End users won't use the header. Email clients will use the header when you hit the report spam or unsubscribe buttons they will display.

[calfuris]

Users don't need to be aware of the header, they just need to use a client that knows what to do with it.