Email Setup

Sendmail Installation

Centmin Mod can be configured to install Sendmail during the initial setup or it can be installed manually via YUM/DNF package manager.

To install Sendmail via the Centmin Mod menu:

centmin
# Select option 13 to install Sendmail

Alternatively, if you prefer Postfix as your MTA, you can install it manually:

yum -y install postfix
systemctl enable postfix
systemctl start postfix

DNS Records

Proper DNS records are essential for email deliverability. Without them, emails sent from your server are likely to be flagged as spam or rejected entirely. The three key DNS record types for email authentication are SPF, DKIM, and DMARC.

SPF (Sender Policy Framework)

SPF records specify which mail servers are authorized to send email on behalf of your domain. Add a TXT record to your domain's DNS:

Type: TXT
Host: @
Value: v=spf1 ip4:YOUR_SERVER_IP -all

# SendGrid
v=spf1 ip4:YOUR_SERVER_IP include:sendgrid.net -all

# Mailgun
v=spf1 ip4:YOUR_SERVER_IP include:mailgun.org -all

# Amazon SES
v=spf1 ip4:YOUR_SERVER_IP include:amazonses.com -all

DKIM (DomainKeys Identified Mail)

DKIM adds a digital signature to outgoing emails, allowing the recipient's mail server to verify that the email was legitimately sent and has not been tampered with. DKIM uses a public/private key pair:

• The private key is stored on your mail server and used to sign outgoing messages.
• The public key is published as a DNS TXT record so recipients can verify the signature.

Type: TXT
Host: selector._domainkey.yourdomain.com
Value: v=DKIM1; k=rsa; p=YOUR_PUBLIC_KEY

DMARC (Domain-based Message Authentication)

DMARC builds on SPF and DKIM to tell receiving mail servers what to do when authentication checks fail. It also provides reporting so you can monitor email authentication results.

Type: TXT
Host: _dmarc.yourdomain.com
Value: v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com; pct=100

Reverse DNS (PTR Record)

A PTR record maps your server's IP address back to your domain name. Many mail servers check for a valid reverse DNS entry and will reject mail from IPs without one. PTR records are typically configured through your VPS or hosting provider's control panel, not your DNS provider.

Testing Email

After installing Sendmail or Postfix and configuring your DNS records, test that your server can send email correctly.

Command Line Test

Send a test email from the command line:

echo "Test email body" | mail -s "Test Subject" you@example.com

PHP mail() Function Test

Create a temporary PHP script to verify that mail() works from your web applications:

<?php
$to      = 'you@example.com';
$subject = 'PHP Mail Test';
$message = 'This is a test email sent from PHP mail().';
$headers = 'From: webmaster@yourdomain.com' . "\r\n" .
           'Reply-To: webmaster@yourdomain.com' . "\r\n" .
           'X-Mailer: PHP/' . phpversion();

if (mail($to, $subject, $message, $headers)) {
    echo 'Email sent successfully.';
} else {
    echo 'Email sending failed.';
}
?>

Check Mail Logs

Monitor the mail log to verify emails are being sent and to diagnose delivery issues. See the configuration files page for log file locations.

# View mail log (CentOS/RHEL/AlmaLinux/Rocky Linux)
tail -f /var/log/maillog

# Check mail queue
mailq

Transactional Email Services

For production websites, using a dedicated transactional email service is strongly recommended over local Sendmail/Postfix. These services provide better deliverability, reputation management, analytics, and compliance with email regulations.

Most services can be configured as an SMTP relay in your Postfix or Sendmail configuration, or used directly via their API from your PHP applications using libraries like PHPMailer or SwiftMailer.

# Example: SendGrid SMTP relay via Postfix
relayhost = [smtp.sendgrid.net]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt
header_size_limit = 4096000

@yourdomain.com Email Hosting

For receiving email at your domain (e.g., info@yourdomain.com), it is strongly recommended to use a third-party email hosting provider rather than running a mail server on your web server. Benefits include:

• Portability — Your email is uninterrupted when migrating between VPS or dedicated servers.
• Reduced resource usage — Less disk and CPU consumption on your web server.
• Reliability — Dedicated mail infrastructure with redundancy and spam filtering.
• Security — Particularly important for domains using HTTPS SSL certificates that require domain-validated email verification.

Recommended Providers

Troubleshooting

Common email delivery issues and their solutions: