Javamath-discuss - A general mailing list for discussion about mathematical software development in Java.
JISCmail - Mailing lists in mathematics and statistics for the UK academic community.
Math Forum: Public Discussions - Group topics include general math, education, geometry, software, calculus reform, research and recreations.
Math Help Forum - A discussion forum for students and teachers of mathematics at school, college and advanced levels, including homework help for students.
Math is Fun Forum - A discussion forum for K-12 math students and teachers, with a focus on learning and teaching math the fun way.
Maths is Toothpaste - Mathematics is useless on its own, it only has a function when used with something else (i.e. a toothbrush). An online discussion.
Maths-Education - Email forum for those working in mathematics education to share ideas and experiences, and request information.
Undernet Math - Topica email list serving the users of the IRC channel #math on the Undernet, for discussion and challenging puzzles.
WebMath - A mailing list for those interested in mathematics on the World Wide Web.
Yahoo Groups : Erdos - A group for proposing problems, sharing ideas, discussing areas of research and reviewing papers and books of interest. [Requires Yahoo! membership]