First giveaway is that they haven't got the guts to post their real name ... and then they give a fake email address;

Recipient address: nimbo@yahoo.com
Reason: SMTP transmission failure has occurred
Diagnostic code: smtp;554 delivery error: dd This user doesn't have a yahoo.com account (nimbo@yahoo.com) [-5] - mta456.mail.mud.yahoo.com
Remote system: dns;mx2.mail.yahoo.com (TCP|167.206.4.204|33179|4.79.181.136|25) (mta456.mail.mud.yahoo.com ESMTP YSmtp service ready)