Mailing lists are a kind of online discussion group.
People subscribe to a list on a topic of interest by sending a simple command by Internet e-mail.
Any message which is sent to a mailing list on a listserver is then forwarded by e-mail to everyone on that list. There are literally thousands of lists covering every imaginable topic, from aerobics to zoology, including many specifically for language teaching. In addition to sharing practical teaching ideas and solutions to common problems, members have discussed testing, discrimination, and job hunting. These lists have slightly different commands for subscribing to them. You can usually tell which kind of listserver it is from the address given for subscribing.