When you use services like Sendgrid, having a spam report will automatically prevent future emails being deliverable, third parties and intermediaries do this precisely to protect their email reputation.

Marking spam may not be immediately be a death knell within Gmail, Hotmail, etc, but because of the potential impact from being marked as spam, virtually everything treats it like a death knell.

This is fine for me, my service is entirely opt-in, and if someone hits the spam button it risks impacting other users who _want_ the email, so I am not bothered that this person effectively unsubbed themselves and killed their account.