Problem on Mail server --- Mail server could not connect to the internet

This morning around 10, suddenly the office email server is inaccessible from the outside. Staff who are outside can notconnect to webmail office. I initially thought because the traffic is being filled, so that all unused bandwidth resulting in slow access to webmail.

But after I checked, ping mailserver from outside, but the resultRTO. Then I try to check ping to the router from the mail server, the results are good. Then I try to ping from the router to the internet,were normal. Wow why this happened.

So I continued an intense checks on the mail server machine.Starting from checking MTA postfix, antivirus, configuration and allwere normal. Quite confusing too ... When I try to restart it with theNIC:
command: # / etc / init.d / networking restart all the results returned to normal.

Strange indeed ... because the machine is no problem to ping to anywhere except the internet. Grateful now back to normal.