0

How to use sendmail as a backup MX/backup mail server


This is a quick guide on how to use sendmail as a backup MX server. If you want to use qmail as a backup MX/backup mail server, please see our Qmail as backup MX guide here.

 

1. Installing sendmail

If you do not have sendmail installed, you can install it using your OS package manager. In this example, we use yum on CentOS:

yum install sendmail

 

2. Configuring the sendmail service

First off, we want to make sure it auto-starts upon reboot:

chkconfig sendmail on

By default, sendmail will only listen on localhost; for this example we will set it to listen on all interfaces instead:

1. Open /etc/mail/sendmail.cf

2. Find the line starting with DaemonPortOptions and then modify it so it looks like this:

DaemonPortOptions=Port=smtp,Addr=0.0.0.0, Name=MTA

 

3. Configuring sendmail to run as backup MX/backup mail server

First, we will need to modify the sendmail access file.

1. Open the access file:

vim /etc/mail/access

2. For every domain that you want to allow this sendmail instance to serve as a backup mail server for, add the following line (replace DOMAIN.com with your real domain name):

To:DOMAIN.com                            RELAY

3. Next, you will need to specify which mail route this sendmail instance will attempt to deliver mail to (replace DOMAIN.com with your real domain name):

DOMAIN.com smtp:mail.DOMAIN.com

4. Finally, we will recreate the database files:

makemap hash /etc/mail/mailertable.db < /etc/mail/mailertable
makemap hash /etc/mail/access.db < /etc/mail/access

5. Make sure to restart sendmail so that our new configuration is taken in to effect:

/etc/init.d/sendmail restart

 

4. Update DNS

Now that you have configured your sendmail service to act as a backup mail server, you will need to update your DNS so that other mail servers know that you have a backup MX.

If you have not already, create a DNS A record for the backup mail server, eg: mail-backup.DOMAIN.com

Next, create a new MX record that points to your DNS name for the backup mail server with a higher priority number than the primary mail server. Remember, the higher the priority number, the less precedence it has, eg in order of preference:

DOMAIN.com MX 10 mail.DOMAIN.com
DOMAIN.com MX 50 mail-backup.DOMAIN.com

 

Now that you have configured sendmail and your DNS, you should now have a backup MX configured ! If you have any issues, questions or concerns, please comment and I will assist where I can.

 

Random Posts Recent Comments

  • Tony Says:

    Thanks it works! Just close the cmd windows and open a new one...

  • greenhart Says:

    I found another way around it. For the /format switch I used: /format:"%WINDIR%\system32\wbem\en-...

  • Jari Aalto Says:

    To determine OS, you can also use command lsb_release(1). See the options how to extract only part o...

  • shadovice Says:

    thanks! it worked like a charm, although there is still minor typo remained: rpm -Uvh http://downlo...

  • Joh Says:

    Great, thank you. Also works with the new version and Centos 6.3 without test repo, just install ...

  • sierprinsky Says:

    Muchas gracias por tu aporte :)...

  • kilby Says:

    The listed solution worked fine for me under Win7 64bit Though I had to run the copy as Asministr...

  • Viper5112 Says:

    The files are already in the C:\Windows\SysWOW64\wbem\en-US and they need to be in the system32 fold...

  • slowmOoh Says:

    Thanks...

  • Jørgen Says:

    @Jordan, I had the same problem also on Windows 7 64 bits. It worked for my user account and Admini...

Tag Cloud

backup mail backup mail server backup mailserver backup mx cd burner control multiple computers with one keyboard and mouse control panel DAG disk benchmark disk performance test DNS DNS check enable dag repo free cd burner free DNS check hdd benchmark http proxy install keyboard over network kloxo kloxo 64-bit kvm lxadmin lxadmin-master lxlabs mouse over network mtr ping plotter proxy proxy hide IP qmail repo RPM rpmforge share keyboard and mouse over network share keyboard over network share mouse and keyboard share mouse over network software kvm squid squid hide IP squid proxy trace traceroute tracert