iRedmail installation: Please configure a fully qualified domain name

ERROR : Please configure a fully qualified domain name

Solution :
1)set hostname in /etc/host (e.g. 127.0.0.1    mail.ubuntu.com      mail      localhost )
2)And also by using command line
       hostname mail.ubuntu.com 


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***************************** WARNING ***********************************
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*                                                                       *
* Below file contains sensitive infomation (username/password), please  *
* do remember to *MOVE* it to a safe place after installation.          *
*                                                                       *
*   * /home/user/iredmail/iRedMail-0.8.7/config
*                                                                       *
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  Would you like to use firewall rules provided by iRedMail now?
Select no : it is not recommended link .