From b7c15c31519dc44c1f691e0466badd556ffe9423 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 18:18:56 +0200 Subject: Adding upstream version 3.7.10. Signed-off-by: Daniel Baumann --- html/ETRN_README.html | 374 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 374 insertions(+) create mode 100644 html/ETRN_README.html (limited to 'html/ETRN_README.html') diff --git a/html/ETRN_README.html b/html/ETRN_README.html new file mode 100644 index 0000000..f1d728f --- /dev/null +++ b/html/ETRN_README.html @@ -0,0 +1,374 @@ + + + + + + +Postfix ETRN Howto + + + + + + + +

Postfix ETRN Howto

+ +
+ +

Purpose of the Postfix fast ETRN service

+ +

The SMTP ETRN command was designed for sites that have intermittent +Internet connectivity. With ETRN, a site can tell the mail server +of its provider to "Please deliver all my mail now". The SMTP server +searches the queue for mail to the customer, and delivers that mail +by connecting to the customer's SMTP server. The mail is +not delivered via the connection that was used for sending ETRN. +

+ +

As of version 1.0, Postfix has a fast ETRN implementation that +does not require Postfix to examine every queue file. Instead, +Postfix maintains a record of what queue files contain mail for +destinations that are configured for ETRN service. ETRN service +is no longer available for domains that aren't configured for the +service.

+ +

This document provides information on the following topics:

+ + + +

Other documents with information on this subject:

+ + + +

Using the Postfix fast ETRN service

+ +

The following is an example SMTP session that shows how an SMTP +client requests the ETRN service. Client commands are shown in bold +font.

+ +
+
+220 my.server.tld ESMTP Postfix
+HELO my.client.tld
+250 Ok
+ETRN some.customer.domain
+250 Queuing started
+QUIT
+221 Bye
+
+
+ +

As mentioned in the introduction, the mail is delivered by +connecting to the customer's SMTP server; it is not sent over +the connection that was used to send the ETRN command.

+ +

The Postfix operator can request delivery for a specific customer +by using the command "sendmail -qRdestination" and, with +Postfix version 1.1 and later, "postqueue -sdestination". +Access to this feature is controlled with the authorized_flush_users +configuration parameter (Postfix version 2.2 and later). +

+ +

How Postfix fast ETRN works

+ +

When a Postfix delivery agent decides that mail must be delivered +later, it sends the destination domain name and the queue file name +to the flush(8) daemon which maintains per-destination logfiles +with file names of queued mail. These logfiles are kept below +$queue_directory/flush. Per-destination logfiles are maintained +only for destinations that are listed with the $fast_flush_domains +parameter and that have syntactically valid domain names.

+ +
+ + + + + + + + + + + + + + + + + +
Postfix
+delivery
agent		 -(domain, queue ID)-> Postfix
+flush
daemon		 -(queue ID)-> One logfile
+per eligible
domain
+ +
+ +

When Postfix receives a request to "deliver mail for a domain +now", the flush(8) daemon moves all deferred queue files that are +listed for that domain to the incoming queue, and requests that +the queue manager deliver them. In order to force delivery, the +queue manager temporarily ignores the lists of undeliverable +destinations: the volatile in-memory list of dead domains, and +the list of message delivery transports specified with the +defer_transports configuration parameter.

+ +

Postfix fast ETRN service limitations

+ +

The design of the flush(8) server and of the flush queue +introduce a few limitations that should not be an issue unless you +want to turn on fast ETRN service for every possible destination. +

+ + + +

Configuring the Postfix fast ETRN service

+ +

The behavior of the flush(8) daemon is controlled by parameters +in the main.cf configuration file.

+ +

By default, Postfix "fast ETRN" service is available only for +destinations that Postfix is willing to relay mail to:

+ +
+
+/etc/postfix/main.cf:
+    fast_flush_domains = $relay_domains
+    smtpd_etrn_restrictions = permit_mynetworks, reject
+
+
+ +

Notes:

+ + + +

To enable "fast ETRN" for some other destination, specify:

+ +
+
+/etc/postfix/main.cf:
+    fast_flush_domains = $relay_domains, some.other.domain
+
+
+ +

To disable "fast ETRN", so that Postfix rejects all ETRN requests +and so that it maintains no per-destination logfiles, specify:

+ +
+
+/etc/postfix/main.cf:
+    fast_flush_domains =
+
+
+ +

Configuring a domain for ETRN service only

+ +

While an "ETRN" customer is off-line, Postfix will make +spontaneous attempts to deliver mail to it. These attempts are +separated in time by increasing time intervals, ranging from +$minimal_backoff_time to $maximal_backoff_time, and should not be +a problem unless a lot of mail is queued.

+ +

To prevent Postfix from making spontaneous delivery attempts +you can configure Postfix to always defer mail for the "ETRN" +customer. Mail is delivered only after the ETRN command or with +"sendmail -q", with "sendmail -qRdomain", or with "postqueue +-sdomain"(Postfix version 1.1 and later only),

+ +

In the example below we configure an "etrn-only" delivery +transport which is simply a duplicate of the "smtp" and "relay" +mail delivery transports. The only difference is that mail destined +for this delivery transport is deferred as soon as it arrives. +

+ +
+
+ 1 /etc/postfix/master.cf:
+ 2   # =============================================================
+ 3   # service type  private unpriv  chroot  wakeup  maxproc command
+ 4   #               (yes)   (yes)   (yes)   (never) (100)
+ 5   # =============================================================
+ 6   smtp      unix  -       -       n       -       -       smtp
+ 7   relay     unix  -       -       n       -       -       smtp
+ 8   etrn-only unix  -       -       n       -       -       smtp
+ 9 
+10 /etc/postfix/main.cf:
+11   relay_domains = customer.tld ...other domains...
+12   defer_transports = etrn-only
+13   transport_maps = hash:/etc/postfix/transport
+14
+15 /etc/postfix/transport:
+16   customer.tld     etrn-only:[mailhost.customer.tld]
+
+
+ +

Translation:

+ + + +

Testing the Postfix fast ETRN service

+ +

By default, "fast ETRN" service is enabled for all domains that +match $relay_domains. If you run Postfix with "fast ETRN" service +for the very first time, you need to run "sendmail -q" once +in order to populate the per-site deferred mail logfiles. If you +omit this step, no harm is done. The logfiles will eventually +become populated as Postfix routinely attempts to deliver delayed +mail, but that will take a couple hours. After the "sendmail +-q" command has completed all delivery attempts (this can take +a while), you're ready to test the "fast ETRN" service. + +

To test the "fast ETRN" service, telnet to the Postfix SMTP +server from a client that is allowed to execute ETRN commands (by +default, that's every client), and type the commands shown in +boldface:

+ +
+
+220 my.server.tld ESMTP Postfix
+HELO my.client.tld
+250 Ok
+ETRN some.customer.domain
+250 Queuing started
+
+
+ +

where "some.customer.domain" is the name of a domain that has +a non-empty logfile somewhere under $queue_directory/flush.

+ +

In the maillog file, you should immediately see a couple of +logfile records, as evidence that the queue manager has opened +queue files:

+ +
+
+Oct  2 10:51:19 myhostname postfix/qmgr[51999]: 682E8440A4:
+    from=<whatever>, size=12345, nrcpt=1 (queue active)
+Oct  2 10:51:19 myhostname postfix/qmgr[51999]: 02249440B7:
+    from=<whatever>, size=4711, nrcpt=1 (queue active)
+
+
+ +

What happens next depends on whether the destination is reachable. +If it's not reachable, the mail queue IDs will be added back to +the some.customer.domain logfile under $queue_directory/flush. +

+ +

Repeat the exercise with some other destination that your server +is willing to relay to (any domain listed in $relay_domains), but +that has no mail queued. The text in bold face stands for the +commands that you type:

+ +
+
+220 my.server.tld ESMTP Postfix
+HELO my.client.tld
+250 Ok
+ETRN some.other.customer.domain
+250 Queuing started
+
+
+ +

This time, the "ETRN"" command should trigger NO mail deliveries +at all. If this triggers delivery of all mail, then you used the +wrong domain name, or "fast ETRN" service is turned off.

+ +

Finally, repeat the exercise with a destination that your mail +server is not willing to relay to. It does not matter if your +server has mail queued for that destination.

+ +
+
+220 my.server.tld ESMTP Postfix
+HELO my.client.tld
+250 Ok
+ETRN not.a.customer.domain
+459 <not.a.customer.domain>: service unavailable
+
+
+ +

In this case, Postfix should reject the request +as shown above.

+ + + + -- cgit v1.2.3