Ars Mathematica

News and discussions on the mathematical arts.

http://www.arsmathematica.net/

JISCmail

Mailing lists in mathematics and statistics for the UK academic community.

http://www.jiscmail.ac.uk/mailinglists/category/Maths_&_Statistics.html

Javamath-discuss

A general mailing list for discussion about mathematical software development in Java.

http://lists.sourceforge.net/lists/listinfo/javamath-discuss

Math Forum: Public Discussions

Group topics include general math, education, geometry, software, calculus reform, research and recreations.

http://mathforum.org/kb/forumindex.jspa

Math Help Forum

A discussion forum for students and teachers of mathematics at school, college and advanced levels, including homework help for students.

http://www.mathhelpforum.com/

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.

http://www.mathisfunforum.com/

MathOverflow

A forum to ask and answer research level mathematics questions.

http://mathoverflow.net/

Maths-Education

Email forum for those working in mathematics education to share ideas and experiences, and request information.

http://lists.nottingham.ac.uk/mailman/listinfo/maths-education

My Math Forum

Active forum for a better understanding of mathematics. Includes puzzles and riddles and some solved problems.

http://www.mymathforum.com/

Undernet Math

Topica email list serving the users of the IRC channel #math on the Undernet, for discussion and challenging puzzles.

http://lists.topica.com/lists/undernet-math/

WebMath

A mailing list for those interested in mathematics on the World Wide Web.

https://mail.cms.math.ca/mailman/listinfo/webmath

Yahoo Groups : Erdos

A group for proposing problems, sharing ideas, discussing areas of research and reviewing papers and books of interest. [Requires Yahoo! membership]

http://tech.groups.yahoo.com/group/Erdos/

Yahoo Groups : Maththeorists

Discussions relating to number and mathematics philosophy.

http://tech.groups.yahoo.com/group/maththeorists/

Yahoo Groups: Math For Fun

Focuses on solving challenging math problems.

http://tech.groups.yahoo.com/group/mathforfun/