Simple Email Form

I want to put a simple box requesting an email address on my site, which in turn will send to a designated email account, which will then auto respond with the information they have requested. I know how to set up the autoresponder. I just can’t seem to find out what code to use for the form. Can anyone tell me how to make a box like I described, where all they enter is an email address and will allow me to set up an autorepsonder to handle the replies. Thanks to anyone who can help me out.

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