The unsubscribe header in the inbox

This is the small "unsubscribe" link some clients show at the top of a message, next to the sender name.

What it is for

It gives the recipient an obvious exit. Without that exit the nearest button is "report spam" — which costs you far more.

It is no longer optional

The large providers require it from bulk senders. Without this header your delivery chances drop, whatever else you do.

It has to work

A link that exists but does not process the request is worse than none. The unsubscribe must take effect quickly and without an extra step.

Do not fear it

Yes, you will lose a few more contacts. Those contacts would have complained instead, and a complaint costs more than a departure.

Check it

Send yourself a test and see whether the link appears. Many senders assume it is there without ever verifying.