How to Configure Sendmail for SMTP Relay with Port 587 ?

Introduction

Configuring Sendmail to act as an SMTP relay with port 587 allows you to relay outgoing emails through a specific server. This setup is commonly used for scenarios where you need to send emails from a server that may not have direct internet access. Below are step-by-step instructions on how to set up Sendmail for this purpose.

Prerequisites

1. Access to a Linux server.

2. Root or sudo privileges.

3. Basic knowledge of working with the command line.

Steps to Configure Sendmail for SMTP Relay with Port 587

Install Sendmail: Use the package manager to install Sendmail along with the necessary configuration files.

    apt-get install sendmail sendmail-cf

Install SASL authentication service: If not already installed, install SASL (Simple Authentication and Security Layer) for authentication purposes.

    apt-get install sasl2-bin

Configure SASL: Edit the SASL configuration file to enable the service.

    vim /etc/default/saslauthd

Set START=yes.

Set Authorization Information: Define authentication credentials in the /etc/mail/authinfo file.

    AuthInfo:abcd.com "U:abcd@gmail.com" "1234" "M:PLAIN"

Update Sendmail Configuration: Edit the Sendmail configuration file to include SMTP relay setup and authentication mechanisms.

    vi /etc/mail/sendmail.mc

Add the following lines:

    define(`RELAY_MAILER_ARGS', `TCP $h 587')dnl define(`ESMTP_MAILER_ARGS', `TCP $h 587')dnl define(`SMART_HOST', `mail.irsis.ph')dnl define(`confAUTH_MECHANISMS', `EXTERNAL 
    GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl FEATURE(`authinfo',`hash /etc/mail/authinfo')dnl

Update Configuration Files: Regenerate the Sendmail configuration file and update authentication database.

    cd /etc/mail m4 sendmail.mc >sendmail.cf makemap hash authinfo < authinfo

Restart Sendmail Service: Restart the Sendmail service to apply the changes.

   /etc/init.d/sendmail restart

Send Test Email: Verify the configuration by sending a test email.

   echo "mail" | mail -s "Hello" abcd@gmail.com

Conclusion

By following these steps, you can successfully configure Sendmail to act as an SMTP relay with port 587, allowing your server to relay outgoing emails through a designated SMTP server. This setup ensures proper authentication and secure transmission of emails.

Remember to replace placeholders such as abcd.com, abcd@gmail.com, 1234, and mail.irsis.ph with your actual domain, email address, password, and SMTP server information respectively.