Security considerations when creating an email form on the web

Question

I know I have to consider about
mail header injection,

and are there more thing that
I need to know before I make form mail thing?

I want mail, and I feel that
I have to set up form mail thing
in my page, but I heard that
mail thing is dangerous if I do not consider all security things.

Answer 1

1- avoid spam, use captcha or other thing to prevent spam.

the link talk about it : http://stackoverflow.com/questions/42076/are-you-human-or-how-to-prevent-spam

2 - Prevent Duplicate Submissions