SMTP Protocol

Table of Contents

Introduction

SMTP Relay

Using Standard Email Clients

SMTP Protocol Introduction

In addition to the HTTP API, Mailgun servers also support the standard SMTP protocol. You can send email using SMTP with or without TLS.

You will need to refer to the standard library documentation for the language of your choice to learn how to you the SMTP protocol. Below are some links for a few popular languages:

• Ruby SMTP
• Python SMTP
• JavaMail API

SMTP Relay

You can configure your own mail server to replay mail via Mailgun (example below). To do so, you will need the following three variables on the Control Panel.

• Your SMTP username
• Your SMTP password
• SMTP host name mail server (these instructions will use smtp.mailgun.org as an example)

You have an SMTP username and password for each domain you have at Mailgun. To send mail from a particular domain, use the proper credentials.

Postfix Instructions

You must configure a relay host with SASL authentication, as shown:

# /etc/postfix/main.cf:

mydestination = localhost.localdomain, localhost
relayhost = [smtp.mailgun.org]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = static:postmaster@mydomain.com:password
smtp_sasl_security_options = noanonymous

# TLS support
smtp_tls_security_level = may
smtpd_tls_security_level = may
smtp_tls_note_starttls_offer = yes

When using TLS encryption, make sure Postfix knows where to locate the CA database for your Linus distribution:

smtpd_tls_key_file = /etc/ssl/private/smtpd.key
smtpd_tls_cert_file = /etc/ssl/certs/smtpd.crt
smtpd_tls_CApath = /etc/ssl/certs

Exim Instructions

For more information, see Exim's documentation authenticated by outgoing SMTP. You will need to configure "smarthost" for your Exim setup.

Also make sure to configure login credentials (in your /etc/exim/passwd.clinet):

# In your exim.conf:
# In routes configuration:
mailgun:
        driver = manualroute
        domains = ! +local_domains
        transport = mailgun_transport
        route_list = * smtp.mailgun.org byname

# In transports configuration:
mailgun_transport:
        driver=smtp
        hosts_require_auth = <; $host_address
        hosts_require_tls = <; $host_address
        ```

Also make sure to cinfigure login credentials (in your  /etc/exim/passwd.client):

```JSON
*.mailgun.org:username:password

Sendmail Instructions

Define the smarthost in your sendmail.mc before mailer definitions:

## Mailgun
define(`SMART_HOST', `smtp.mailgun.org')dnl
FEATURE(`authinfo', `hash /etc/mail/authinfo')dnl
# optional, see http://www.sendmail.org/m4/features.html before enabling:
# FEATURE(`accept_unresolvable_domains')dnl
# FEATURE(`accept_unqualified_senders')dnl
# execute: make -C /etc/mail
## Mailgun

Specify login credentials in your authinfo:

AuthInfo:smtp.mailgun.org "U:<LOGIN>" "P:<PASSWORD>" "M:PLAIN"

Run the following command and then restart sendmail:

make -C /etc/mail

Using Standard Email Clients

Standard email clients like Thunderbird or Outlook can also be used to send mail.

Settings for sending mail:

SMTP server: smtp.mailgun.org