Exchange 2013: Cannot Receive mail from Internet

Hello,

I had an Exchange 2010 well running on my network (mysociety.local); now I do a new installation of Exchange 2013 on news machines on mysociety.intra (My Configuration is: 1 AD+DNS server: SRV-AD and 1 Exchange 2013 Server member: MAIL).

All of old machines and exchange 2010 are retired.

Now my Problem is:

I can send/receive in internal; I am able to send mail to Internet, but i am unable to receive and i have no NDR

But my external domain name is still mysociety.com; The MX is still also mail.mysociety.com and still pointed to my external IP. There is no changes in my firewall.

PS: If i replace the old configuration with Exchange 2010 everthing come ok

Please Need a help

Thanks.