Sendmail Extended Queue Groups is an m4 file that can be used to add extended queue groups to Sendmail 8.12.x. Extended queue groups allow administrators to choose multipe queue groups based on the sender, recipient, or sender and recipient pair. This improves upon the default plain queue groups feature, which can only operate on recipients.
Smail is a Mail Transport Agent. Its job is to accept mail messages from sources on the local machine, or from remote hosts, and deliver those messages to the appropriate destinations, be they to remote hosts or to files or programs on the local machine. Smail is designed to be mostly compatible with sendmail but uses a much simpler configuration scheme.