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Mail Setup Guide (Linux Servers)

This document explains two supported ways to enable email sending from a Linux server:

  1. Direct delivery from the server itself (no external SMTP relay)
  2. Delivery via an external SMTP server (relay / smarthost)

Both approaches work with tools like mail, mailx, sendmail, and monitoring scripts (such as RAID alerts).

1. Direct Mail Delivery (Server → Recipient MX)

This method sends email directly from your server to the recipient's mail server using SMTP.

This is equivalent to how cPanel/Exim works by default.

✔ Characteristics

  • No external SMTP provider
  • No authentication
  • Uses the server's IP address
  • Likely to be marked as spam (expected for testing)
  • Best for internal alerts, testing, or isolated environments

1.1 Install Postfix and mail utilities

apt update
apt install postfix mailutils

During installation (or via reconfiguration), choose:

  • General type of mail configuration: Internet Site
  • System mail name: your hostname (e.g. server.example.com)

If Postfix was already installed but not configured:

dpkg-reconfigure postfix

1.2 Start and verify Postfix

systemctl restart postfix
systemctl status postfix

You should see:

Active: active (running)

1.3 Test direct mail sending

echo "Direct mail test from $(hostname)" | \
mail -s "Mail test" you@example.com

Check logs:

tail -f /var/log/mail.log

Expected behaviour:

  • Postfix looks up recipient MX
  • Attempts SMTP delivery
  • Mail may be delayed, spam-filtered, or rejected — this is still success

1.4 Common issues (direct delivery)

Port 25 blocked

Some hosting providers block outbound traffic on port 25 by default, which prevents direct mail delivery.
HyberHost does not block port 25 for new customers. We only restrict it if an IP address generates abuse complaints, ensuring responsible use while allowing direct mail for testing and alerts.

Test:

nc -vz gmail-smtp-in.l.google.com 25

If blocked, direct delivery will fail.

Reverse DNS mismatch

Not required for testing, but affects deliverability.

hostname -f

1.5 Recommended usage

✔ Monitoring alerts (RAID, disk, uptime) ✔ Internal systems ✔ Temporary testing

❌ Transactional or user-facing email

2. Sending Mail via an External SMTP Server (Relay)

This method relays all outgoing mail through a third-party SMTP server.

Examples:

  • Google Workspace
  • Microsoft 365
  • Mailgun
  • SendGrid
  • ISP SMTP servers

✔ Characteristics

  • Requires authentication
  • Better deliverability
  • Works even if port 25 is blocked
  • Recommended for production alerts

2.1 Option A: Postfix with SMTP relay

Install Postfix

apt install postfix mailutils

Choose:

  • General type: Internet Site

Configure relay settings

Edit:

nano /etc/postfix/main.cf

Add or modify:

relayhost = [smtp.example.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

Create SMTP credentials

nano /etc/postfix/sasl_passwd

Format:

[smtp.example.com]:587 username:password

Secure and apply:

chmod 600 /etc/postfix/sasl_passwd
postmap /etc/postfix/sasl_passwd
systemctl restart postfix

Test

echo "Relay test" | mail -s "SMTP relay test" you@example.com

2.2 Option B: msmtp (lightweight, no daemon)

This is ideal for simple alerting scripts.

Install

apt install msmtp msmtp-mta

Configure /etc/msmtprc

defaults
auth           on
tls            on
logfile        /var/log/msmtp.log

account relay
host smtp.example.com
port 587
user username
password password
from alerts@example.com

account default : relay

Secure it:

chmod 600 /etc/msmtprc

Test

echo "msmtp test" | mail -s "msmtp test" you@example.com

3. Choosing the Right Method

Use case Recommended method
Quick testing Direct delivery (Postfix)
RAID / system alerts Direct or relay
VPS with blocked port 25 SMTP relay
Production alerting SMTP relay
No daemon wanted msmtp

4. How This Integrates with Scripts

All methods above support:

echo "message" | mail -s "subject" recipient@example.com

Which means no script changes are required.

Your monitoring scripts only need:

  • mail binary
  • A working MTA or relay

5. Troubleshooting

Check logs:

tail -f /var/log/mail.log

Check sendmail path:

which sendmail

Check Postfix config:

postconf -n