Short URL Expansion to prevent banned-url circumvention.
 

A spammer has unlimited URL shorteners at their disposal to shorten their banned URL.

You can't block all URL shorteners.

But you can send URLs through an API like http://longurl.org/ or curl them with

$ curl http://shortened-url.com -w "%{redirect_url}"
-> http://destination-url.com

I think the easiest implementation would be to write a plugin as a cron-job that replaces URLs in the privatemessage table with their redirected URLs.

Luxury features would include:

- auto-flag user or private message for moderation
- go through vB's Edit Post mechanism so that censors are applied
- expose some simple controls that limit the scope of privatemessages that will get replaced. For instance, in my case, I would only do it for users with less than 25 posts.

I couldn't find an existing mod with this functionality, but it would be an incredible spam deterrent and disarm repeat-spammers.