MeTA1 is a message transfer agent that has been designed with
these main topics in minds:
MeTA1 consists of five main modules of which only one runs as root:
* mcp: the main control program is similar to inetd(8):
it starts all other MeTA1 modules and watches over their execution.
mcp runs as root in order to bind to port 25 and to change the uid
of the processes it starts.
* smtps: the SMTP server receives e-mails.
* smtpc: the SMTP client sends e-mails.
* smar: the address resolver provides lookups in various maps
including DNS for mail routing.
* qmgr: the queue manager controls the flow of e-mails through the
SMTP servers and clients.