[edent]

They're also really useful for evading spam filters. I found[1] a bunch of government domains with open redirects.

Spammers were sending out emails containing links to `example.gov.uk/redirect?url=dodgy-viagra.ph` - and certain spam filters were trained to whitelist "trusted" domains.

You also see a lot of open redirect abuse on forums - especially where they're configured to only show the first few dozen characters of a link.

[1] https://www.openbugbounty.org/researchers/edent/