Blocking a person from receiving emails

Site URL: https://thecrochetcouch.com

Occasionally I like to offer my email subscribers a code for a free pattern.  There's always at least one person that tries to abuse it and uses several different email addresses to get more than one free item.

If I see them I cancel the order(s) and that typically stops them from continuing as I guess they feel "found out".  I would like to not ever email these people again but can't seem to figure out a way to do it.  

Can somebody please answer this question, I have a similar problem...

Thank you in advance for answering the above question.

regards,

Jürgen