That's a bit system dependent, check the log and see what it shows as 
the ip address when they connect via ipv6, you could then use that
string in a wild card rule to block access g_deny....

     ChrisP.


On 27/01/2016 3:26 a.m., surgemailHIDDEN@etwinsite.com wrote:
> Is their a process to block ipv6 smtp connections from some ip ranges..
> Forcing them to communicate over ipv4 only?