Try to find out the email function

Try to find out the email function

I setup a new CustomModul which included the lookup field for contacts (incl. email address).  I also setup a mail template for this CustomModul. Now I want to send an email to the client. Get the error: Unable to send email as the CustomModul does not have eigher an email address or a secound email address. I tried the BigDeal email in the contact, what works fine.