DNS Configuration Guide

This document explains how to correctly configure DNS for domains or subdomains that will use the Mail Forwarding Service, so they can be safely:

• accepted by Postfix

• authorized in the database (domain table)

• used by the API and UI

DNS must be configured before inserting the domain into the database. If DNS is wrong, mail delivery, forwarding, SPF, or DMARC will fail.

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Step 1 — PTR / Reverse DNS (mandatory, done at provider)

PTR (reverse DNS) must be configured first, directly at your VPS or hosting provider.

Generic model

CopyIPv4  ->  mail.your-domain.tld
IPv6  ->  mail.your-domain.tld

mail.your-domain.tld  ->  IPv4
mail.your-domain.tld  ->  IPv6

Real example (current setup)

CopyPTR: 161.97.146.91              -> mail.abin.lat
PTR: 2a02:c207:2298:1997::1     -> mail.abin.lat

mail.abin.lat -> 161.97.146.91
mail.abin.lat -> 2a02:c207:2298:1997::1

Important notes:

• PTR is not configured in Cloudflare or normal DNS panels

• PTR must match the hostname used by Postfix (myhostname)

• Missing or mismatched PTR is the #1 reason for outbound mail rejection

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Step 2 — DNS records for a domain

Target domain example: example.com Mail host: mail.abin.lat

Required records

SPF (recommended)

Copyexample.com TXT "v=spf1 ip4:<YOUR_IPV4> ip6:<YOUR_IPV6> -all"

Example using current IPs:

Copyexample.com TXT "v=spf1 ip4:161.97.146.91 ip6:2a02:c207:2298:1997::1 -all"

DMARC (recommended)

Copy_dmarc.example.com TXT "v=DMARC1; p=none; rua=mailto:dmarc@example.com; fo=1"

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Step 3 — DNS records for a subdomain

Target subdomain: sub.example.com Mail host: mail.abin.lat

Required records

SPF

Copysub.example.com TXT "v=spf1 ip4:<YOUR_IPV4> ip6:<YOUR_IPV6> -all"

DMARC

Copy_dmarc.sub.example.com TXT "v=DMARC1; p=none"

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Step 4 — Authorize the domain in the database

After DNS is fully propagated, insert the domain (or subdomain) into the domain table.

Example:

CopyINSERT INTO domain (name, active) VALUES ('example.com', 1);

For subdomains:

CopyINSERT INTO domain (name, active) VALUES ('sub.example.com', 1);

Once inserted:

• Postfix will accept mail for the domain

• The API can create aliases

• The UI can expose the domain (if listed in NEXT_PUBLIC_DOMAINS)

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Common mistakes / important notes

• PTR missing or wrong → outbound mail rejected

• MX pointing to wrong host → mail never reaches your server

• SPF not matching server IP → forwarded mail may fail DMARC

• Domain added to DB before DNS → mail will fail even if alias exists

• Using a hostname without A/AAAA → Postfix cannot identify itself correctly

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Summary (checklist)

Before adding a domain to the database:

• PTR → mail.your-domain.tld

• mail.your-domain.tld → A / AAAA

• MX → mail.your-domain.tld

• SPF includes server IP(s)

• DMARC present (at least p=none)

• Domain inserted into domain table