strange email

i got this email with a stange email address inviting me to join a msn group for online dating and might contain adult stuff .i wanted to know if it were someone i knew but going under a different address(because why would they invite me)so added them to msn and found their profile without any info,so i decided to send an email asking who they were ,but and error occured saying this email doesnt exit (how is this possible.)how can someone send an email from an email that doesnt exist !!!!!!!.can u help me please .anyway if anyone knows how to check here is the email address of the strange person([email protected])and their user name is [email protected]