ETRN(8) Maintenance Commands and Procedures ETRN(8)

NAME

etrn - start mail queue run

SYNOPSIS

etrn [-b] [-v] server-host [client-hosts]

DESCRIPTION

SMTP's ETRN command allows an SMTP client and server to interact, giving
the server an opportunity to start the processing of its queues for
messages to go to a given host. This is meant to be used in start-up
conditions, as well as for mail nodes that have transient connections to
their service providers.


The etrn utility initiates an SMTP session with the host server-host and
sends one or more ETRN commands as follows: If no client-hosts are
specified, etrn looks up every host name for which sendmail(8) accepts
email and, for each name, sends an ETRN command with that name as the
argument. If any client-hosts are specified, etrn uses each of these as
arguments for successive ETRN commands.

OPTIONS

The following options are supported:

-b
System boot special case. Make sure localhost is accepting SMTP
connections before initiating the SMTP session with server-host.

This option is useful because it prevents race conditions between
sendmail(8) accepting connections and server-host attempting to
deliver queued mail. This check is performed automatically if no
client-hosts are specified.


-v
The normal mode of operation for etrn is to do all of its work
silently. The -v option makes it verbose, which causes etrn to
display its conversations with the remote SMTP server.

ENVIRONMENT VARIABLES

No environment variables are used. However, at system start-up,
svc:/network/smtp:sendmail reads /etc/default/sendmail. In this file, if
the variable ETRN_HOSTS is set, svc:/network/smtp:sendmail parses this
variable and invokes etrn appropriately. ETRN_HOSTS should be of the
form:

"s1:c1.1,c1.2 s2:c2.1 s3:c3.1,c3.2,c3.3"


That is, white-space separated groups of server:client where client can
be one or more comma-separated names. The :client part is optional.
server is the name of the server to prod; a mail queue run is requested
for each client name. This is comparable to running:

/usr/lib/sendmail -qR client


on the host server.

EXAMPLES

Example 1: Using etrn

Inserting the line:


ETRN_HOSTS="s1.example.com:clnt.example.com s2.example.com:clnt.example.com"


in /etc/default/sendmail results in svc:/network/smtp:sendmail invoking
etrn such that ETRN commands are sent to both s1.example.com and
s2.example.com, with both having clnt.example.com as the ETRN argument.


The line:


ETRN_HOSTS="server.example.com:client1.example.com,client2.example.com"


results in two ETRN commands being sent to server.example.com, one with
the argument client1.example.com, the other with the argument
client2.example.com.


The line:


ETRN_HOSTS="server1.example.com server2.example.com"


results in set of a ETRN commands being sent to both server1.example.com
and server2.example.com; each set contains one ETRN command for each host
name for which sendmail(8) accepts email, with that host name as the
argument.

FILES

/etc/mail/sendmail.cf
sendmail configuration file


/etc/default/sendmail
Variables used by svc:/network/smtp:sendmail

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Stable |
+--------------------+-----------------+

SEE ALSO

attributes(7), sendmail(8)


RFC 1985

NOTES

Not all SMTP servers support ETRN.

November 22, 2021 ETRN(8)