There are a vast number of discussion forums that operate through e-mail, in much the same way as eMSSA does.
Below you will find details of some of the better-known forums. Make sure you come back often, as I will be adding to them over time.
Note also that lists come and go, and so some of these links may become invalid over time. If you find that a list no longer exists, please e-mail me.
This forum's focus is on so-called "Internal strength". It is, so say the list owners, the deciding factor as to whether a style is internal or external, soft or hard.
Styles which are discussed on this forum include taiji (t'ai chi), bagua, xingyi (hsing-i). The debate centres around body mechanics and not qi (ch'i, or internal energy), because that way they can ensure that something is deemed "correct" if you can achieve results with it. They argue not that qi doesn't exist, but rather that it is so ambiguous that you can't tell if you're doing your techniques correctly or not.
This list, although it can be quite harsh to some people who oppose the "system" (but they do this for reasons I clarified above) it an absolute must for people who are serious about their internal arts.
This is a discussion group for people interested in Aikido. (No further information available.)
This is one of the oldest martial art discussion forums on the Internet, having begun in 1993. It was designed specifically for those individuals and organizations that are involved in Traditional Japanese or Okinawan Karate. However, there is a special exception made for individuals who have not yet chosen a path.
This discussion group is one of many available for Kung Fu practitioners. (No further information available.)
Tae Kwon Do
This forum's is for people interested in debating Tae Kwon Do specifically. (No further information available.)
This is a discussion forum dedicated to martial artists practising Korean styles, like Tang Soo Do, Hapkido, HwaRang Do, Taekwondo, Kuk Sool, etc. It comes in single-mail as well as digest versions. To find out more, send an e-mail to email@example.com, and type in the body of the message: "info the_dojang-digest" (without the inverted commas). You could also ask for "info the_dojang" if you're not interested in the digest version.
Internal Strength List
This is another list dedicated to talking about internal strength, with a focus on the structural and mechanical aspects. It is slightly less technical that the Neijia list (see above).