==== Required information ====
- iRedMail version: 0.8.6
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Linux/BSD distribution name and version: Debian 7.4
- Related log if you're reporting an issue:
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I noticed that there were no sql table backups being performed on the server even though there was an entry in the root crontab that had been created during installation to run backup_mysql.sh every day at 03:30. 

Running the script manually worked fine but it was not being executed by the crontab job.  A little research revealed this in man crontab:

"cron requires that each entry in a crontab end in a newline  character. If  the  last entry in a crontab is missing the newline, cron will consider the crontab (at least partially) broken and refuse to install it."

So if there is no blank line at the end of the crontab file, it will never execute.  Sure enough adding a blank line at the end of the crontab file solved the problem and the backup is now occurring on schedule.

This appears to be a Debian (and Debian derivative) issue only.  I don't see that warning in the CentOS man page nor does the issue seem to be present in CentOS.