multiple domains in postfix – adding of local host

hello i have everything running on postfix but can not recieve mail. mail does arrive at postfix (not a dns issue), but mail seems to go to a strange address. if i send mail to me@new_domain.com it gets sent to menew_domaincom@localhost.com my virtual file is as follows me@new_domain.com menew_domaincom menew_domaincom is the short name for the account set up in system preferences. please note i am using a client version of 10.3 please be specific i am new to unix