SEC.01
The playbook
The run starts read-only: the recon probes decide what happens next. The steps that follow are adapted to the distribution and state found — a real machine is rarely clean.
- 01recondistro (apt or dnf) and EL version
- 02reconPostfix already installed? version? active?
- 03reconanother MTA (exim4, sendmail) active? installing Postfix would replace it
- 04reconrelayhost/SASL already configured? does Postfix already receive mail (inet_interfaces)?
- 05recontable type (hash or lmdb) and existing sasl_passwd
- 06reconwho listens on 25 and on which interface
- 07actInstall Postfix + SASLverify
- 08actWrite the SMTP credentials (600)verify
- 09actConfigure the relaydestructiveverify
- 10actCheck and restart Postfixverify
- 11actTest email (only if a recipient is provided)verify
SEC.02
What it verifies
Each step ships its own check. The run only moves on when the check passes, so what the recipe reports as done is what is actually on the server.
- 01verifyInstall Postfix + SASLVerified by
postconf -h mail_version - 02verifyWrite the SMTP credentials (600)Verified by
stat -c '%a %n' /etc/postfix/sasl_passwd* - 03verifyConfigure the relayVerified by
postconf -h relayhost smtp_sasl_auth_enable - 04verifyCheck and restart PostfixVerified by
systemctl is-active postfix - 05verifyTest email (only if a recipient is provided)Verified by
journalctl -t postfix/smtp --since '-3 min' --no-pager | tail -3
SEC.03
Guardrails
Non-negotiable instructions the run must respect, whatever it finds on the server.
The SMTP password only goes into /etc/postfix/sasl_passwd (600), never into main.cf. It must never be displayed or logged: no cat/grep/head of sasl_passwd, no set -x, no echo, and it appears in no other command nor in any verify. Back up main.cf before changing it. Do not replace exim4/sendmail without consent. An outbound relay opens no firewall port.
SEC.04
Variables
What you choose before launching — the recipe fills in the rest.
| Name | Meaning |
|---|---|
| ${relayhost} | Smarthost |
| ${username} | SMTP user |
| ${password} | SMTP password |
| ${test_to} | Test email recipient (optional) |
| ${from_address} | Sender verified with the relay (optional) |
SEC.05
How a recipe runs in Servor
Servor is zero-knowledge: the platform cannot execute anything on its own. When you launch this recipe, a run reads the reconnaissance, plans the steps and asks for your approval. Each approved command is signed by your browser — with a key the server never sees — then relayed verbatim to the agent, which verifies the signature locally before executing.
search by intent — type “firewall”, get ufw
- 01Read-only reconnaissance before any change
- 02Every command signed by your browser, approved by you
- 03Each step verified before the run moves on, every run kept in the history
SEC.06
Deploy on Servor button
Maintain SMTP relay (Postfix) or a project that needs it? Put this button in your README or on your site: one click and your users install it on their own server.
Dark background
Light background[](https://servor.app/deploy/setup-postfix-relay)SEC.07
More mail recipes
Verified recipe
Run this recipe on your server
Connect a server, launch the recipe, and approve each step as Servor executes and verifies it. Free plan, no card required.