There's nothing more annoying than clicking that 'unsubscribe' link at the bottom of your email only to be asked to login first. I know it sucks when people opt-out of your transactional emails, but deal with it and let people unsubscribe with one click. If you do this you may even get some valuable feedback.

If your transactional email provider doesn't have a single-click unsubscribe option, find another service. I recommend every developer test out what a recipient sees.

Sincerely,

Users of the Internet