i can't send to another mail server

==== Required information ====
- iRedMail version: 0.8.4
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): mysql
- Linux/BSD distribution name and version: ubuntu 12.4 LTS
- Related log if you're reporting an issue:
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Hi...after i sent a message to myEmail@gmail.com from a iredmail server all what i got is : Domain not found

any an idea ?

thank you .