The IRC channels are the place to go if you want immediate answers to your questions. Be advised that they are a pretty informal place and you won't always find someone who can answer your questions, but with them being a common hangout for developers, auto-editors and other active users, the chances are high! They are #musicbrainz and #musicbrainz-devel on irc.freenode.net.
The mailing lists are discussion centres for different purposes. The most active and important for users are the Users list (for questions and general discussion) and the Style list (where decisions about most changes to MusicBrainz are taken by the community). There is also a Developers list, for more technical discussion about development. If you prefer a forum-like interface, the lists have also a Nabble interface.
The MusicBrainz forums are a good place for asking and answering specific questions if you don't want to subscribe to a mailing list. It has two sections, support and discussion, with five forums in total. Note that the style discussion in the forum is not a substitute for the Style mailing list, and while it is sometimes useful for discussion, the decisions are taken in the list following the proposal procedure.
Our bug tracker, powered by Jira, is the place to go if you want to report a bug or ask for a new feature. For bugs, please always explain what happened and what you were trying to do, with the URLs of any page(s) involved. Note that some new features and changes will need the approval of the community through the style mailing list (see our proposal procedure).
The MusicBrainz wiki is mainly a source of documentation, but it can sometimes be used for communication. Every page has its associated discussion page, and you can leave messages for other wiki users in their user talk pages. Be advised though that not everyone checks the discussion pages often, so forums, mailing lists and the IRC are probably better places to go.
Direct MusicBrainz email
If you need to talk with someone with special privileges, you can reach the MusicBrainz staff directly at firstname.lastname@example.org.
Note that MusicBrainz does not provide support for taggers in the Tagger Affiliate Program such as Magic MP3 Tagger or Yate Music Tagger. Contact and support information for these applications can be found on their respective pages. Also, if you just want to sell us advertising, don't make the effort to send an email, we'll ignore it anyway.
If you believe that MusicBrainz violates your copyright, you may report a copyright violation. Please note that MusicBrainz provides data about recordings, not the music itself. If you find your music listed in MusicBrainz it does not mean that we have access to or provide access to the music files themselves. If you still think that we're infringing your copyright, you must provide us with a link to where you can download the infringing copyright from our website. If you cannot provide us a link, we cannot help you.
The MusicBrainz blog is where announcements about the MusicBrainz Database, Picard and the community are published. While comments are open on it, letting people provide short feedback, it is not really convenient for in-depth discussions, which are usually held in the mailing lists.
You can follow the MusicBrainz twitter (@MusicBrainz) to get some updates about the project. It usually mirrors the contents of the blog, but we will sometimes tweet about smaller issues that are not worthy of a full blog post. You can ask questions to it, but it is not the best place for it, so if you're already here, you might as well use the forums or IRC!
More or less once a year, the developers and part of the community meet in real life for a MusicBrainz Summit! New summits are usually announced in the blog well in advance.