SPAM Emails produced automatically by 'robots' that scan the Internet for contact forms on websites.  They send emails through any form.  All busy sites get them. 

Our options are:

 1 -  to simply delete as they arrive.  If you often receive the same email or from the same sender you can set up a rule to auto delete.

 2 - add a capture form.

A capture form (sample here: http://www.britnett.co.uk/contactus.html) asks the sender to populate one box with visible numbers/letters before they can send an email.  Only a human can see the numbers/letters therefore allows an email.  Robots cannot 'see' the capture box.  Although some technology use  Optical Character Recognition that reads the numbers/letters and populates the box.  That is why the numbers/letters are distorted.