Postfix Smart Host Setup for mySMTP

You need your SMTP username, password, and relay hostname from your mySMTP setup email.

Before you start

Have these details ready:

Setting	Value
Relay host	Your relay hostname, e.g. `relayxx.mysmtp.com`
Port	587
Encryption	STARTTLS
Username	Your mySMTP SMTP username
Password	Your mySMTP SMTP password

Use the exact relay hostname from your setup email. relayxx.mysmtp.com is only an example.

Install required packages

Debian / Ubuntu
RHEL / CentOS / Rocky

sudo apt update
sudo apt install libsasl2-modules

sudo yum install cyrus-sasl-plain

Configure the smart host

Edit main.cf

Open /etc/postfix/main.cf in your editor and add or update these lines:

relayhost = [relayxx.mysmtp.com]: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

Replace relayxx.mysmtp.com with your actual relay hostname.

Create the SASL password file

Create /etc/postfix/sasl_passwd with this content:

[relayxx.mysmtp.com]:587    username:password

Replace relayxx.mysmtp.com, username, and password with your actual values.

Hash the password file

Run:

sudo postmap /etc/postfix/sasl_passwd

This creates sasl_passwd.db. For security, restrict permissions on both files:

sudo chmod 600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db

Restart Postfix

sudo systemctl restart postfix

Test the connection

Send a test email using the mail or sendmail command:

echo "Test message body" | mail -s "Test subject" -a "From: you@yourdomain.com" recipient@example.com

If your system does not have the mail command, install mailutils (Debian/Ubuntu) or mailx (RHEL).

Check the mail log for delivery status:

sudo tail -f /var/log/mail.log

Look for a successful connection to your relay hostname and a status=sent entry.

Troubleshooting

Authentication failed (SASL authentication failed)

Double-check the username and password in /etc/postfix/sasl_passwd. Run sudo postmap /etc/postfix/sasl_passwd again after any change, then restart Postfix.

Connection timed out

Check that outbound traffic on port 587 is allowed by your firewall. Try port 2525 if port 587 is blocked:

relayhost = [relayxx.mysmtp.com]:2525

Update the port in /etc/postfix/sasl_passwd as well, then run sudo postmap /etc/postfix/sasl_passwd and restart Postfix.

TLS handshake failed

Confirm smtp_tls_security_level = encrypt is set in main.cf. Some older systems may need smtp_tls_wrappermode = yes for port 465, but mySMTP uses STARTTLS on port 587.

Relay access denied

Make sure the sender address uses a domain authenticated for your mySMTP account. See DNS settings quick explainer.

For more error codes, see Common SMTP errors.

Home

API & Webhooks

Before you start

Install required packages

Configure the smart host

Test the connection

Troubleshooting

​Before you start

​Install required packages

​Configure the smart host

​Test the connection

​Troubleshooting

Before you start

Install required packages

Configure the smart host

Test the connection

Troubleshooting