Courier benchmarks:

a) Local ESMTP loopback test.
   Hardware:  ASUS P2B-DS Dual PentiumII-450 motherboard.
              FAST SCSI-II disk (Quantum Fireball)
              256MB RAM.
              Network card: NE2000 clone, 10mbps ethernet.

   Software:  Two copies of Courier running locally:
              Courier S is the sending server.
              Courier R is the receiving server.

              Default options for both Courier S and R, with the following
              exceptions:
              Both copies of Courier are configured for 40 ESMTP connections
              maximum (Courier R has the max sessions per C block
              bumped up to 40).
              Courier R is configured to issue forward/reverse IP address
              DNS query for every connecting session (default configuration).
              Courier R is configured to check each connection against two
              DNS blacklists (default configuration).
              Note -- all DNS queries were over an analog dialup 28.8
              connection (but the test ran locally).
              Courier R is configured to check IDENT for each connection
              (default).
              Courier R has SMTP spam filtering enabled (but no spam filter
              is actually used for this test).
              Courier R had BOFHCHECKDNS disabled, so the sender's address
              wasn't checked in DNS.

              Both versions of Courier had certain modules linked with the
              ElectricFence malloc debugger, which introduces its own overhead.
              Basically, there was some additional overhead in this test.  In
              the real world the timings would probably be faster by a hair.

   Test consists of sending messages from Courier S to Courier R as fast
   as possible.  Courier R is configured to treat *.example.com as a local
   address.  Courier S is configured to send all mail to *.example.com to the
   same IP address as what's assigned to the local NIC card, which is
   functionally identical to sending all trafic through 127.0.0.1.

   Because multiple hostnames are used, Courier S is tricked into opening
   multiple ESMTP clients in parallel, instead of queueing up everything for
   a few connections.  The following script was used to generate test
   messages (hostnames and account names changed to protect the innocent):
  
	for n in 1 2 3 4 5 6 7 8 9 10
	do
	for f in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
	do
		env - /tmp/courier/bin/sendmail \
			-f sender@example.com \
		recipient-foo-$f@$f.foo.example.com <<EOF
	From: sender
	To: recipient
	Subject: test $f

	test $f
	EOF
	done
	done

   A global .courier-foo-default file is used in the recipient account
   to dump all mail into the same Maildir.  As you can see, there are 20
   different recipient addresses scattered across 20 different hostnames.
   Courier's default configuration opens a maximum of four connections to
   the same recipient hostname, so this test can theoretically use up to 80
   parallel connections, however both Courier R and S were configured to
   use no more than 40, causing contention.  Ten copies of each message
   were sent.

   Total run time: 1 min 5 seconds for 196 messages.  Four messages were
   stuck waiting on a stalled DNS query, and were delivered when it timed out
   and retried, 50-75 seconds later.

   Mail logs show that there were 57 total ESMTP connections made.  So,
   Courier's message scheduler was able to reuse most ESMTP sessions, but the
   scheduler did close some connections along the way.

   NOTE that each ESMTP connection required four DNS lookups.  So, in the
   space of 1 min 5 seconds Courier was able to deliver 196 messages and
   issue 53*4=216 DNS lookups over a severely bandwidth-limited line.