Question : 421.4.3.2 service not available

I have just set up the new small business server 2008
and I have a problem receiving e-mail from external clients
but internally we can send e-mail to each other fine and from a command line-also send e-mail to an internal e-mail box
I'm using the standard SMTP port 25
whenever anybody tries from externally they get 421.4.3.2 service not available
I have checked my firewall and port 25 is open
the IP address is 78.32.179.162 if you have the time to try it
any help would be much appreciated

please be patient as I do not have a e-mail server and I will have to keep looking back here for your reply

Thank you in advance

Answer : 421.4.3.2 service not available

OK I have found out what it was:
open the management console. go to server management, hub transport. There are two default connectors there, ione is nanamed default. double click the default conector, network tab, and then and the address for remoute servers opened this up and now all is now working