ezmlm is an easy-to-use, high-speed mailing list manager for qmail.

ezmlm lets users set up their own mailing lists within qmail's address
hierarchy. A user, Joe, types

   ezmlm-make ~/SOS ~/.qmail-sos joe-sos isp.net

and instantly has a functioning mailing list, joe-sos@isp.net, with all
relevant information stored in a new ~/SOS directory.

ezmlm takes advantage of qmail's VERPs to reliably determine the
recipient address and message number for every incoming bounce message.

ezmlm is reliable, even in the face of system crashes. It writes each
new subscription and each new message safely to disk before it reports
success to qmail.

ezmlm doesn't mind huge mailing lists. Lists don't even have to fit into
memory. ezmlm hashes the subscription list into a set of independent
files so that it can handle subscription requests quickly. ezmlm uses
qmail for blazingly fast parallel SMTP deliveries.