man/man8/etrn.8

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 ETRN 8 "November 22, 2021"
 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.