There are two Linux/MIPS-oriented mailing lists:
This mailing list currently has the most traffic. It is especially of interest as a good number of active developers are subscribed to this list.
This is an announcement only mailing list to which a message for every CVS commit into linux-mips.org's, CVS archive of the Linux/MIPS community, is being sent. This allows following the development as it happens.
Subscription to this lists is handled via Ecartis (ecartis@linux-mips.org), just send an email with the words subscribe <list-name>. In order to unsubscribe, send unsubscribe linux-mips. Sending the word help will reveal further secrets about the advanced use of Ecartis. At http://www.linux-mips.org/ecartis you'll also find a web-based interface to Ecartis.
Note linux-mips.org is using the ECN TCP extension as described in RFC 3168. The bug is known for years yet still defective firewalls that are dropping TCP SYN packets with ECN bits set are in use. If you can reach linux-mips.org yet don't receive any email from any of the linux-mips.org mailing lists you may have this problem.
The archives for these two lists in UNIX mbox format are located on ftp.linux-mips.org in /pub/linux/mips/archives. A fully searchable archive in HTML format of the above lists and some Linux/MIPS related historic lists can be found at http://www.linux-mips.org/archives/.
There is an IRC channel named #mipslinux for Linux/MIPS which may be found on irc.freenode.net.