re-order pages. add page on lmtp.

This commit is contained in:
Christoph Haas 2025-08-24 23:53:04 +02:00
parent b97d7b03da
commit 759ed36026
5 changed files with 215 additions and 53 deletions

View file

@ -0,0 +1,155 @@
---
title: LMTP
lastUpdated: 2025-08-24
slug: ispmail-trixie/lmtp
sidebar:
order: 167
---
import { Aside } from "@astrojs/starlight/components";
import StepListReceive from "../../../components/StepListReceive.astro";
<StepListReceive currentStep={5} />
Glad to see that you are still with me. We are very close to receiving our first email. If you feel lost, please review
the [slideshow](/ispmail-trixie/big-picture/) from earlier in this guide.
As explained in the previous section, Postfix speaks SMTP and receives the email from the internet. Postfix could even
save the email to a mailbox on disk. But instead we will use Dovecot for the final delivery. Actually Dovecot's main
purpose is to let users fetch their email using the IMAP protocol. But it provides additional features we can use as
well.
So we need tell Postfix to hand over the incoming email to Dovecot. The communication between Postfix and Dovecot will
happen using LMTP the [local mail transfer protocol](https://en.wikipedia.org/wiki/Local_Mail_Transfer_Protocol).
LMTP is a variant of SMTP with fewer features. It is meant for email communication between internal services that trust
each other.
## Dovecot listens to LMTP
There's nothing to do for you here. I just want to tell you how it works. By default Dovecot has this section in its
`/etc/dovecot/conf.d/10-master.conf` file:
```
service lmtp {
unix_listener lmtp {
}
}
```
So Dovecot has already put a socket into `/var/run/dovecot/lmtp` where it is ready to receive LMTP connections. A socket
is similar to a TCP port but it's only available for other processes running on same system. So nothing to do.
## Postfix talks to Dovecot using LMTP
The “_virtual_transport_” in Postfix defines the service to use for delivering emails to the local system. Dovecot has
created a socket file and is ready to listen to incoming LMTP connections. We just need to tell Postfix to send emails
there. So please run:
```sh
postconf virtual_transport=lmtp:unix:/var/run/dovecot/lmtp
```
The syntax looks crazy, but its actually simple. You just told Postfix to use the LMTP protocol. And that we want to
use a UNIX socket on the same system (instead of a TCP connection). And the socket file is located at
`/var/run/dovecot/lmtp`.
## Enable server-side mail rules
TODO: move to optional chapter
## Send a test mail locally
Finally we are ready for our first email. Using the `swaks` command you can create a test email to `john@example.org`
and send it to Postfix:
```sh
swaks --server localhost --to john@example.org
```
If all goes as planned, you will see an SMTP dialog like this:
```
=== Trying localhost:25...
=== Connected to localhost.
<- 220 mail ESMTP Postfix (Debian)
-> EHLO mail
<- 250-mail
<- 250-PIPELINING
<- 250-SIZE 10240000
<- 250-VRFY
<- 250-ETRN
<- 250-STARTTLS
<- 250-ENHANCEDSTATUSCODES
<- 250-8BITMIME
<- 250-DSN
<- 250-SMTPUTF8
<- 250 CHUNKING
-> MAIL FROM:<root@mail>
<- 250 2.1.0 Ok
-> RCPT TO:<john@example.org>
<- 250 2.1.5 Ok
-> DATA
<- 354 End data with <CR><LF>.<CR><LF>
-> Date: Sun, 24 Aug 2025 21:08:59 +0000
-> To: john@example.org
-> From: root@mail
-> Subject: test Sun, 24 Aug 2025 21:08:59 +0000
-> Message-Id: <20250824210859.021444@mail>
-> X-Mailer: swaks v20240103.0 jetmore.org/john/code/swaks/
->
-> This is a test mailing
->
->
-> .
<- 250 2.0.0 Ok: queued as 2742B221FA
-> QUIT
<- 221 2.0.0 Bye
=== Connection closed with remote host.
```
If you see a `250 2.0.0 Ok: queued as…" near the end of this dialog, then Postfix has received the email successfully.
Check if Postfix managed to pass the email to Dovecot:
```sh
journalctl -n 10 -u dovecot
```
The line you are looking for looks like:
```
Aug 24 21:36:22 mail dovecot[23214]: lmtp(john@example.org)<…><…>: msgid=<20250824213622.023221@mail>: saved mail to INBOX
```
Does it say `saved mail to INBOX`? Awesome. The email should be visible in John's home directory. Check it:
```sh
find /var/vmail/example.org/john
```
Does it look like this?
```
/var/vmail/
/var/vmail/example.org
/var/vmail/example.org/john
/var/vmail/example.org/john/Maildir
/var/vmail/example.org/john/Maildir/maildirfolder
/var/vmail/example.org/john/Maildir/new
/var/vmail/example.org/john/Maildir/new/1756071382.M198387P23222.mail,S=635,W=655
/var/vmail/example.org/john/Maildir/cur
/var/vmail/example.org/john/Maildir/tmp
/var/vmail/example.org/john/Maildir/dovecot-uidvalidity.68ab85d6
/var/vmail/example.org/john/Maildir/dovecot.index.log
/var/vmail/example.org/john/Maildir/dovecot-uidvalidity
/var/vmail/example.org/john/Maildir/dovecot.index.cache
/var/vmail/example.org/john/Maildir/dovecot-uidlist
/var/vmail/example.org/john/Maildir/dovecot.list.index.log
```
The important file here is `…/Maildir/new/1756071382.M198387P23222.mail,S=635,W=655`. The numbers will look differently
on your system. But this is the actual mail that got delivered. You can view it with `cat` and will find the test email
you just sent using `swaks`.
Don't worry about the other files like `maildirfolder` or the files that sound like `dovecot…`. Those help Dovecot keep
track of the mailbox. You can safely ignore them.