Subject: Re: sendmail configuration
To: Erik E. Fair <>
From: Don Lewis <>
List: current-users
Date: 11/03/1995 15:59:36
On Nov 3, 11:38am, "Erik E. Fair"  (Time Keeper) wrote:
} Subject: Re: sendmail configuration
} Load average based limiters have been in sendmail since the beginning; the
} conf file options are
} Ox - "load average at and above which sendmail will just queue mail,
} instead of doing delivery."
} OX - "load average at and above which sendmail will withdraw SMTP service."

[ deleted ]

} However, system load average reacts slowly to changes in load, and
} particularly with the Internet being several million hosts, I believe it is
} much better to precisely limit the number of processes doing SMTP service,
} against the possibility that "too many" peers (for some value of "too
} many") decide to contact my server at the same time.

>From the contrib/xla/README file in the sendmail 8.x distribution:

         XLA - Extended Load Average design for Sendmail R6

          Christophe Wolfhugel - Herve Schauer Consultants

WARNING:  this extension is supplied as a contribution to Sendmail.
Should you have trouble, questions, please contact me directly, and
*not* the Sendmail development team.


Sendmail currently furnishes a limitation mecanism which is based on
the system load average, when available.  Experience has prooven that
this was not sufficiant for some particular situations, for example
if you have slow and/or overloaded links. This can easily cause both
system and network congestions with Sendmail having to handle a large
number of simultaneous sessions on the same overloaded link, causing
most of the SMTP sessions to timeout after a long time.  The system
load average is also generally too slow to react when your system
gets a burst of incoming or outgoing SMTP sessions which on some
stations can easily cause system unavailabilities.

The extended load average module has been designed in order to furnish
a way of limitation the load generated by Sendmail to both your
system and your network. This design can be used either alone or as
complementary to the system load average if your system supports it.

Limitation is based on the number of incoming/outgoing SMTP sessions,
and remote hosts are classified in classes. The system administrator
will define a maximum number of incoming SMTP sessions as well as
a maximum total (incoming + outgoing) sessions for each class of
hosts. A class can be either an individual machine or a network.

When the limit is reached for a given class, all incoming SMTP
connections will be politely refused. When the limit is reached for
all classes, the SMTP connections will be refused by the system
(which one could consider as less politely :)).
On outgoing mail, messages will be queued for delayed processing.

The extended load average parameters are given in the Sendmail
configuration file, and when not present, Sendmail behaves the
usual way.

			---  Truck