veebr0
> Server=IBM X320 with 8 RAM Memory
Don't know what memory that is, but I see a spec for that machine has 512Mb, which is a minimum for a low end sme server. For 180 users I thing 8Gb might be more appropriate, which is perhaps what you mean (???).
> Private Gateway
That will not work as in Private mode you disable all external access. Private mode only allows outgoing data.
Depending how you want your system setup you choose Server & Gateway mode (sme acts as firewall) or Server only mode (behind an existing firewall/router).
> internal domain=company.local
No need to configure a internal domain, that's Windows server parlance and only complicates the setup.
> abc.com
Just give your sme server that name as the Primary (main) domain when you first setup sme server.
> Please send to my if it possible an how to guide in order to implement this.
The howto you seek is already written. It's called the Admin Manual & User Manual, and by clicking on the Wiki link at top of these forums, you will be able to see and read the online manuals. There is a lot of other useful info in the FAQ & Howtos, so see links at top of this page.