Ok

setup is complex as I'm running quite a bit of stuff!!
Basically I have setup DNS in the form of ISC's Bind using views meaning I have an internal view and 2 external views; 1 for my current IP which is static and another for everybody else!! - I don't want to recursively allow anyone unknown or allow the hinted root zone to be looked up by anyone apart from known hosts or me
Zimbra is configured to use DNS instead of NIS or LDAP; if I recall correctly as it's been a while (time to check link I think)
The server is I know underpowered as it's a PIV 3.4GHz Dell desktop system with 1.5GB RAM! However, even with such low specs I could do worse and CPU shouldn't be sky high no??
Also why for the life of me can't I send email from it when I am outside the network?? It should just work on username/password principle shouldn't it?? That's what it did before going haywire, however config hasn't changed meaning it's most likely me at fault somewhere.......
Apologies for 2 questions wrapped up in one but they seem to be related if totally mutually exclusive.