begun writing the section on receiving mails#
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---
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title: Overview
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lastUpdated: 2025-08-09
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slug: ispmail-trixie/overview
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sidebar:
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order: 120
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---
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import "@splidejs/splide/css";
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import { Splide, SplideSlide } from "astro-splide";
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Your mail server will use multiple pieces of software to do its job. I have created a little slideshow to help you
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understand what happens when someone on the internet sends an email to your server. I will provide more slideshows later
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when it comes to fetching and relaying emails. Use the arrows to switch between slides:
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<Splide>
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{Array.from({ length: 24 }, (_, i) => i + 1).map((i) => (
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<SplideSlide>
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<img src={`/big-picture-receive/${String(i).padStart(2, "0")}.svg`} alt={`Slide ${i}`} />
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</SplideSlide>
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))}
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</Splide>
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So:
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- DNS is used to find your mail server
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- Postfix receives emails using SMTP (the Simple Mail Transport Protocol)
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- SQLite stores information about your domains and mail users
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- rspamd checks if it is spam
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- Dovecot saves it to disk
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79
src/content/docs/ispmail-trixie/160-receive-emails.mdx
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79
src/content/docs/ispmail-trixie/160-receive-emails.mdx
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---
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title: Receive emails
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lastUpdated: 2025-08-20
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slug: ispmail-trixie/receive-emails
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sidebar:
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order: 160
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---
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import { Aside } from "@astrojs/starlight/components";
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import "@splidejs/splide/css";
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import { Splide, SplideSlide } from "astro-splide";
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I have created a little slideshow to help you understand the process of receiving an email from a remote mail server.
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Use the arrows to navigate between slides:
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<Splide>
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{Array.from({ length: 24 }, (_, i) => i + 1).map((i) => (
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<SplideSlide>
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<img src={`/big-picture-receive/${String(i).padStart(2, "0")}.svg`} alt={`Slide ${i}`} />
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</SplideSlide>
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))}
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</Splide>
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So:
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- DNS is used to find your mail server. First the MX record. Then the A and/or AAAA record.
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- Postfix receives emails using SMTP (the Simple Mail Transport Protocol)
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- MariaDB stores information about your domains and mail users
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- rspamd checks if it is spam
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- Dovecot saves it to disk
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## DNS
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Let's begin with setting up the DNS records. Say that you want to receive emails for the `example.com` domain. If some
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other mail server on the internet wants to send an email to your server, it looks for two records:
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- **MX record (`example.com`)**
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The MX (Mail Exchange) record tells other mail servers _where to deliver emails_ for the domain `example.com`.
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Instead of pointing directly to an IP address, it points to a **hostname** (for example, `smtp.example.com`).
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MX records also include a **priority value**. If multiple mail servers are listed, the one with the lowest priority
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number is tried first. Others are used as fallback if the first is unavailable.
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- **A / AAAA record (`smtp.example.com`)**
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The hostname specified in the MX record (`smtp.example.com`) must resolve to an IP address so that other mail servers
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know how to reach it.
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- An **A record** maps the hostname to an IPv4 address.
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- An **AAAA record** maps the hostname to an IPv6 address.
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Once resolved, the sending mail server connects to that IP address on **TCP port 25**, which is the standard port for
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email delivery (SMTP).
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<Aside>
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If no MX record is found, the remote mail server will instead directly look for an A or AAAA record of `example.com`.
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</Aside>
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<Aside type="caution">
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The MX record must point to a hostname. It **must not** point to an IP address directly.
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</Aside>
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In zone syntax you would create something like:
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```
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@ IN MX 10 smtp
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smtp IN A 100.64.17.3
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smtp IN A fd7a:115c:a1e0::17
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```
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If possible, also add a PTR record that makes the IP addresses point back to the name `smtp.example.com`. Other mail
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servers may be more likely so flag your sent emails as spam if you do not have a PTR record. Preferable the forward
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(A/AAAA) and reverse (PTR) records match.
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## Postfix
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…
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