How can I configure myhostname to work with Postfix?

There are multiple files involved in setting up a proper Ubuntu server (12.04.x) for email. Here's the list of those as available at the moment in my server.

• /etc/hosts - This file in my Ubuntu server has the following line, among other lines

  127.0.1.1 myhostname.mydomainname.tld myhostname
  

  Note: Please never touch the line that contains 127.0.0.1. It may be generated and / or updated by the web host upon each reboot.

• /etc/hostname - This file in my Ubuntu server has the following content.

  myhostname
  

• /etc/mailname - This file in my Ubuntu server has the following content.

  mydomainname.tld
  

• /etc/postfix/main.cf - This file in my Ubuntu server has the following lines, among others...

  myorigin      = /etc/mailname
  myhostname    = myhostname.mydomainname.tld
  mydestination = localhost, myhostname.mydomainname.tld
  

Once all the above files have the expected content, you may run the following commands to let them all work together while sending emails...

$ sudo hostname -F /etc/hostname
$ sudo service postfix restart

If you have a server, exclusively for email, I'd recommend keeping the hostname as mail. Otherwise, use any hostname and keeping sending the emails as mydomainname.tld using Mandrill.

Make sure, everything works as expected even upon a reboot. You wouldn't want your web host to override any files upon reboot, that may affect the email sending / receiving.

I hope that helps.

Make changes in your /etc/hosts file as below :

<IP>   <FQDN>  <ALIAS>

So in your case it would be :

127.0.0.1  mail.mydomainname.com  mail

then do following changes :

if you are using Ubuntu:

Edit /etc/hostname and change to the new value,

nano /etc/hostname 

if you are using RHEL/CentOS:

Edit: /etc/sysconfig/network

HOSTNAME=mail.mydomainname.com

then you can run following command to apply changes .

hostname mail

then check.