Can't receive emails from another machine

[Stayvoid]

Hello,

I'm using Postfix.
I can send / receive emails from / to localhost via telnet. [1]
But I can't receive emails from another machine.

I guess that there are three variants:
1. Postfix doesn't work properly;
2. Bind doesn't work properly;
3. IPTables doesn't work properly.

I can't be 100% sure but I think that it's not connected with Postfix.
So I have to check Bind or / and IPTables.

I hope that you'll help me to check my Bind settings.
What should I paste?

Thanks

[1] https://help.ubuntu.com/community/Postfix#Testing