SMTP Hosting: Setup and Usage Guide

SMTP (Simple Mail Transfer Protocol) is the standard protocol used to send emails over the internet. If you need to set up an SMTP hosting server for sending emails, this guide will walk you through everything from selecting a provider to configuring your SMTP server.

For closely related mail-stack topics, see Email Hosting Script — Self-Hosted Setup, MX Hosting — Complete Guide, Gmail 550-5.7.1, and Email Rate Limited.

Postfix is a popular SMTP server for sending emails.

Install Postfix

sudo apt update && sudo apt install postfix -y   # Ubuntu/Debian
sudo yum install postfix -y                      # CentOS/RHEL

Configure Postfix

During installation, you will be prompted to choose a type of mail configuration. Select "Internet Site" and set:

• System mail name: yourdomain.com
• SMTP relay: None (if sending directly)

You can manually edit the configuration:

sudo nano /etc/postfix/main.cf

Add or modify:

myhostname = mail.yourdomain.com

mydomain = yourdomain.com

myorigin = $mydomain

inet_interfaces = all

mynetworks = 127.0.0.0/8

relay_domains =

home_mailbox = Maildir/

Save and exit.

Restart Postfix

sudo systemctl restart postfix
sudo systemctl enable postfix

Test SMTP Server

echo "Test email from my SMTP server" | mail -s "SMTP Test" recipient@example.com

For CentOS/RHEL users, Exim is a great alternative to Postfix.

Install Exim

sudo yum install exim -y

Enable Exim

sudo systemctl start exim
sudo systemctl enable exim

Configure Exim

Edit the configuration file:

sudo nano /etc/exim/exim.conf

Modify:

domainlist local_domains = @ : yourdomain.com

Save and restart:

sudo systemctl restart exim

To prevent unauthorized usage, enable SMTP authentication.

Install SASL for Authentication

sudo apt install libsasl2-modules sasl2-bin -y  # Ubuntu/Debian
sudo yum install cyrus-sasl -y                  # CentOS/RHEL

Configure SASL for Postfix

Edit:

sudo nano /etc/postfix/sasl/smtpd.conf

Add:

pwcheck_method: saslauthd

mech_list: PLAIN LOGIN

Restart SASL:

sudo systemctl restart saslauthd
sudo systemctl enable saslauthd

Restart Postfix:

sudo systemctl restart postfix

Once your SMTP server is running, you can configure an email client (e.g., Outlook, Thunderbird, Gmail) to send emails.

SMTP Settings for Email Clients

Setting	Value
SMTP Server	mail.yourdomain.com
SMTP Port	587 (STARTTLS), 465 (SSL), or 25 (Unencrypted)
Username	your_email@yourdomain.com
Password	Your SMTP password
Encryption	TLS or SSL

Example: Configuring Outlook

1. Open Outlook.
2. Go to File > Account Settings > Add Account.
3. Select Manual setup.
4. Choose IMAP or POP.
5. Enter:
   • Incoming mail server: mail.yourdomain.com
   • Outgoing mail server (SMTP): mail.yourdomain.com
   • Username: Your full email address.
   • Password: Your SMTP password.
6. Click More Settings > Outgoing Server, check "My SMTP server requires authentication".
7. Click Advanced and set:
   • SMTP Port: 587 (TLS) or 465 (SSL).

Use Telnet

telnet mail.yourdomain.com 25

Type:

EHLO yourdomain.com

MAIL FROM: <you@yourdomain.com>

RCPT TO: <recipient@example.com>

DATA

Subject: Test Email



This is a test email.

.

QUIT

Use Swaks (SMTP Debugging Tool)

sudo apt install swaks -y

swaks --to recipient@example.com --server mail.yourdomain.com --auth LOGIN --auth-user your_email@yourdomain.com --auth-password yourpassword

Check Postfix Logs

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

Check Exim Logs

sudo tail -f /var/log/exim_mainlog

Common Errors & Fixes

Secure Your SMTP Server