The easiest way to get in touch is to hop on IRC, the Internet Relay Chat system. We're in the #derpibooru channel on PonyChat (irc.ponychat.net). If you have an IRC client installed, click this link to join
If you've not got an IRC client installed on your PC, you can use Ponychat's webchat by clicking this link
If you've got an issue with an image, content on the site, or otherwise want to have a good 'ol natter with us, that's cool. Just drop 'clover the clever at derpibooru.org' an email (remove spaces and replace at with @).
If you have a legal claim to content hosted on this site, want to send us DMCA notices, and so on, well, that's your call. But we're happy to take down stuff which infringes upon copyright without a DMCA if there's a pretty clear case that copyright is being violated. We don't like copyright violation, and will work with you to fix this stuff.
We don't like DMCA trolls who don't actually respect copyright. For legal matters, contact us at the address listed above. We respect the right to fair use of copyright.