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)