Think I'm just missing something basic but I have an exchange 2010 mail server, it's sitting behind a 1941 Cisco router.
Have NAT configured as static.
ip nat inside source static 10.10.10.15 000.000.000.000
where 000.000.000.000 is an external address
all internal computers have internet access, email is flowing successfully.
From any internal computer on the local lan I can successfully telnet to port 25, run ehlo and get a response.
but from any external device i get a connection error when attempting to telnet.