ahmedsa
Did you read the Manual link I posted earlier ?
ie
Please carefully read this
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Chapter13#E-mailIt explains when & why you would use multidrop or ETRN (if you read the text in the images & on the server manager screens).
Your ISP is the entity who determines what the technical settings are for their service (ie the provision of mail & Internet connection), so you need to ask them.
How i hire technical for sme
Ask your local computer store for someone proficient in Linux, that is a starting point.
Look up technical support services in the phone book, just like any other service you would be requiring.
Ask friends, ask other technically minded people.
Ask on this forum, check the Koozali site, it is possible/probable that someone can assist you remotely (for a fee).
One person I am aware of who provides tech support for SME server in Australia is Graeme Robinson, search the forums for him.
Also this which only lists one partner at present, I think they could help you on a commercial basis.
http://www.koozali.org/partners/find-a-partner