This is a C program to do "bulk" mailing.  For input, it takes a file
of recipient addresses (one address per line) and a message (with
headers already attached) to be sent to the recipients.  It sorts the
recipient list by reversed domain (so similar ones sort together),
splits up the recipients into several groups containing no more than N
domains each, creates an SMTP envelope for each group of recipients,
and feeds that envelope to "/usr/sbin/sendmail -bs".