above links posted by technobear will help u for sure
You can add a captcha to your form to protect the spam emails from coming.
this needs a server side and eye verification at the same time.
there are 4-5 ways of adding captcha
if you want to make it very strict than you can make it like a question
count the number of words in this question and multiply it by 12.
but this may be very difficult for normal user as multiplying and counting can take some time as well as they may navigate away from your website
3rd way is to have an image based captcha with random letters but in that case you need a sound version too as some users may face problem with that kind of captcha. some users face hard time to read such letters and i have many friends who are trying to avoid such captcha.
best way is to put the plus and minus or logical captcha
server side validation is used in this code.
doing a quick search on google gave me this as a best result
If you follow above tutorial with video i think you should have it working. it is little bit technical and may take some time but if you copy and paste the code i think it should be working.