[vamin]

It's not generally a significant effect, unsubscribe rates tend to be well under 1%. Most people just ignore emails they don't want.

[thirdsun]

Don't forget the people that abuse the "mark as spam"-button as unsubscribe link. I saw that beahvior with non-techy users - it's often easier to find than the unsubscribe link and has the same effect to them.

[SteveGerencser]

This. The unsub rates I see tend to be measured in tenths of a percent or less.

[paulie_a]

I'd be curious in someone running an experiment that involved the unsubscribe link displayed as prominent as the marketing message.

[patio11]

N = 1, but I used to put it in the second sentence of my emails. The unsubscribe rate was still measured in basis points, although I had an unusually high quality list relative to e.g. most e-commerce shops.