Mailer Daemon

1-A former course mate in Msc PM send me an emailed today. To be honest, that friend is the last person on Earth I expected to give me anything(not in negative connotation). However I am pleased with his still trying to reach me to say Hello.

2-I then check my inbox, Masya Allah, a lot of Mailer Daemon(that is to remind me that the email was not succesfully send) though I did not send anything at the first place!!! So my point was, that particular friend thought I did send him(hence his Hello email to me) a or few spam email but I am not..

3-Cursed all the spammer!!!

p/s-Ymail is a free email account so we know whats type of security they got to offer.