exchange 2003 - outbound mail query

hi i have a small internal network on windows 2003 platform.

note: i am using 2 companies: (just for purposes of practical test)

- isp - specifically for internet access
- 123-reg.co.uk - registrar - used as a test to allow send/receive email externally ie a & mx record added:

a record: 77.102.156.22
mx record: mail.msexchange.gb.net

currently internal network has internet access via isa as usual!!!!! continued as below:

i am currently using a residential type netgear/vmdg480 router - set to 'modem/enable', instead of 'built-in dhcp mode'.

isa 2006 (member server):

internal nic: 10.0.0.9/23
primary dns: 10.0.0.10
dg: none set (due to dns)

external nic: 77.102.156.22/24 - connected to netgear/vmdg480 router direct to internet
primary dns: 194.168.4.100
secondary: 194.168.8.100
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master dc/as/dns/dhcp server: 10.0.0.10/23 (single master dc only)
primary dns: 127.0.0.1
dg: 10.0.0.9

note: ran simple & recursive dns tests: successful

-----------------------------------------------
exchange 2003 (member server): 10.0.0.9/23
primary dns: 10.0.0.10
dg: 10.0.0.9

exchange 2003: nslookup successful
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- installed exchange 2003 - as member server
- all sp's & updates & ran msbpa
- configured esm for 'rus' - ie recipient policy update for:

smtp @ msexchange.gb.net - set as primary

aduc user account: paulf via email address tab: set as:

msexchange.gb.net - set as primary (also)

test 1:

email tests sent/received:

external to internal - inbound successful

- from: tbowyer@eosworks.co.uk  to  paulf@msexchange.gb.net - successful
- from: asl315@315.ru  to  paulf@msexchange.gb.net - successful
- from:  als315@gmail.com  to  paulf@msexchange.gb.net - successful
- from: foster139689@yahoo.co.uk  to  paulf@msexchange.gb.net - unsuccessful

test 2:

internal to external - reply back to above: unsuccessful - all

outstanding issues:

eventviewer - shows smtp/dns /udp - issue & not running

esm: in additonal info it states in: server:\queue - remote dns cannot connect or no bind etc

test 3:

ran internet mail wizard successfully - chose only send internet email outbound, but still cannot send email external as above via test 1/2 - why ?

question 1.

can anyone advise on how i allow internal users to send email externally & the issue of inbound email being received, but (not from my own yahoo account) ?