Sendmail implements a general purpose internetwork mail routing facility. This document explain how to build sendmail with IPv6 support.



You should have a basic knowledge of UNIX and DNS.

The server should allow incoming connections to the SMTP service which will be listening on TCP port 25.

The server should have a fully qualified hostname (FQDN) such as

The hostname should resolve to an AAAA record. It should not be a CNAME.

The MX record for the domain for which you wish to receive mail should point to the hostname of your server.

There should a PTR record for the IP address of your server. Mail from your server may be rejected if there is no reverse DNS.

Installing sendmail

Download the sendmail source code from the sendmail website.

  • Extract the files from the downloaded file.
  • Change the current directory to where the sendmail source code was extracted.
  • Edit devtools/Site/site.config.m4 and add the following statement:


  • Enter the following command:

    sh Build

  • If there are no errors, you may continue with the installation.
  • If you are installing sendmail 8.12.x, 8.13.x, or 8.14.x
    • Verify whether you have a user smmsp. Create the user if it does not exist. The user should not be assigned a login shell.
    • Verify whether you have a group called smmsp.
  • Enter the following command:

    sh Build install

The sendmail binary is now installed. The next step is to configure sendmail.

Configuring sendmail

The main configuration file for sendmail is the /etc/mail/ file. Starting with version 8.12, sendmail uses the /etc/mail/ configuration file for mail submission. The .cf files are complex to understand. It is recommended that you create a .mc configuration file and use the M4 (macro processor) to generate the .cf file.

There are some sample .mc configuration files in the cf/cf/ directory of the sendmail source code. Alternatively, you can use one of the sample configuration files available from this website. You should edit the .mc file with a UNIX text editor such as vi.

  • Change the current directory to cf/cf directory.
  • Copy your .mc configuration file to the current directory as
  • Edit the and add:


  • To generate the, enter the following command:

    sh Build

  • To install the as /etc/mail/ and as /etc/mail/, enter the following command:

    sh Build install-cf

Sample configuration files are available for download on our sendmail installation webpage.


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If you have problems sending or receiving emails; or require technical support for sendmail, we can help you.