R option to sendmail and artifacts

[Beau James {Manager - SW Development - Ultra Networks}]

--> I've been wondering what happens when the server is down or even just
--> busy.  Since the machines with R option are presumably not running a
--> daemon, queueing makes no sense; ie, no daemon to later run the queue.
--> Does sendmail with the R option notify the user of the problem, quietly
--> lose the mail, ...?  Could some of the artifacts be left over because the
--> server was unavailable? 

At least on SunOS 4.0.1, sendmail on the client goes into an infinite
retry loop, attempting to connect to the server, getting "Connection
refused" or similar failures each time.  This continues until the sendmail
daemon on the mail server returns to life to accept the mail.

Can you say, "Peg my client CPU?"

In a large percentage of cases, the mail server and the diskless client's
server are the same machine, so the client tends to be hung anyway when
sendmail is not available on the server.  But if the mail server and disk
server are different machines, or if sendmail is disabled on the disk
server for other reasons, the client loses.

The real performance lose is delivering mail to diskless clients.  It's an
expensive way to get the bits onto the server's disk.  Most of the
performance gain can be had by delivering mail on the server, but still
running the sendmail daemon on the client, so that the mail can be queued
on the client if undeliverable.  As long as mail is being delivered on the
mail server, the client sendmail daemon will rarely be invoked.  It will
end up swapped out, consuming minimal system resources.

Beau James				beau at Ultra.COM
Ultra Network Technologies		{sun,ames}!ultra.com!beau