Our verdict on Postal

Postal is for adult sites that want to run their own sending relay, with their own IPs and send limits, behind a list manager such as listmonk or Mautic. It replaces a hosted Mailgun or Postmark account with a server you manage.

The catch is that deliverability is entirely yours: a clean IP, correct DNS and subscribers who actually opted in.

Postal

Postal server requirements and port 25

Postal runs in Docker on a server dedicated to it, with at least 4 GB of RAM, 2 CPU cores and 25 GB of disk. The database must be MariaDB 10.6 or later. MySQL is not supported, and Postal creates one database per mail server.

Before you pick a provider, check that outbound port 25 is open. The docs note that blocking it is common, and that IPs from big VPS providers such as DigitalOcean or Linode may already sit on blocklists, so you may have to try more than one.

Using Postal as the SMTP server behind a newsletter tool

Postal accepts messages over SMTP or its HTTP API and delivers them. It has no address book, no campaigns and no unsubscribe handling, and the team has said it will not add them. For a newsletter, plug Postal in as the SMTP server behind listmonk, Mautic or phpList.

Keeping Postal emails out of spam

Postal checks the DNS of your sending domains, signs mail with DKIM, keeps a suppression list of addresses that bounce, and enforces per-server send limits. IP pools let you send from different addresses depending on sender or recipient, such as one IP per site. If mail still lands in spam, run a message through a tester such as Mail Tester to find the cause.

Who maintains Postal

Postal started in 2017 at Krystal Hosting, which held the copyright until 2024, when Adam Cooke and Charlie Smurthwaite took it on. The GitHub repository has close to 17,000 stars, version 3.3.7 came out in June 2026, and code was still being pushed in early October 2026. Help comes through GitHub discussions and a Discord server.

Postal strengths and limitations

Strengths

Your own relay, fully under your control.
IP pools per site or sender.
MIT license, free.

Limitations

No subscribers or campaigns.
Dedicated server with port 25 open.
IP reputation to build yourself.
Community help only.

What to pair Postal with

listmonk handles several SMTP servers and picks one by sender domain, which suits a setup with several Postal servers. OpenEMM already ships its own Postfix and needs no Postal beside it.