smtpdcheck - Online in the Cloud

PROGRAM:

NAME

smtpdcheck - check SMTP servers

SYNOPSIS

smtpdcheck [--stop {ip-addr|name}] [--timeout seconds]
[prio:]server [[prio:]server]

DESCRIPTION

smtpdcheck checks to see if SMTP servers are available. The intent is for use on
secondary mail servers, which have no reason to accept mail when the primary server is
available.

The argument consists of a list of server names, each of which may optionally be prefixed
by a numeric MX priority and a colon. (This is exactly the format for MX records returned
by the avenger dns command.) smtpdcheck will attempt to connect to each server in
succession.

If one of the servers specified on the command line is available, smtpdcheck will print
its name to standard output and exit with status 1. If smtpdcheck cannot connect to any
of the servers, it will exit with status 0. If a system error occurs, smtpdcheck will
exit with status 2.

OPTIONS
--stop {ip-addr|name}
Tells smtpdcheck to stop before checking a server with IP address ip-addr or hostname
name. If such a host is encountered in the list of servers and prio is specified,
then smtpdcheck will consider it acceptable for other servers with the same priority
to be available, even if those servers were first in the list. In other words, given
the following arguments:

smtpdcheck --stop s2.domain.com
10:s1.domain.com 10:s2.domain.com
20:s3.domain.com

This command will always succeed, regardless of whether "s1.domain.com" is up, because
"s2.domain.com" has the same priority. On the other hand, the following command will
fail and output "s1.domain.com" if "s1.domain.com" is up:

smtpdcheck --stop s2.domain.com
10:s1.domain.com 20:s2.domain.com
30:s3.domain.com

If a gethostbyname lookup for the argument name fails, smtpdcheck will exit
immediately with status 2.

--timeout {seconds]
By default, smtpdcheck spends 10 seconds probing each server. This includes the time
to do a DNS lookup, to establish a TCP connection to port 25 of the server, and to
read the "220" SMTP code from the server's SMTP greeting message. To use a different
value, specify it with the --timeout option. The value 0 disables the timeout
completely, which is dangerous since smtpdcheck might then end up waiting forever to
read the "220" string.

EXAMPLES

To refuse to relay mail at a secondary MX server when the primary server is not down, you
might place the following in /etc/avenger/secondary (assuming MxLocalRcpt is 1):

dns RECIP_MXES mx "$RECIPIENT_HOST"
setvars
server=`smtpdcheck --stop $MYIP $RECIP_MXES`
test -n "$server" && defer "Please use server $server"

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