bulk_mailer assists with "bulk" mailing, such as large majordomo
lists under sendmail.  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/lib/sendmail -bs".

Splitting the envelopes up allows sendmail to perform delivery in
parallel, so instead of having one large queue entry (for which
sendmail might take awhile to get around to attempting delivery
for some recipients), it has several smaller queue entries.
Depending on your point-of-view, this can still be considered
"cluttering up your mail queue", but it does seem to deliver messages
more quickly to most recipients.
