Is there a way to autorespond a message on a certain condition?
For example when a user checks a checkbox.
Alternatively, when this is not possible or needs (complex) custom code, is it possible to use a not required e-mail field which we use in the Auto Responder tab? I don't know what happens to the Auto Responder when the e-mail is empty?
I'm not aware of accomplishing this within the user interface. You can't add macro's to the fields that work with enabling the auto responder.
I'd think creating a global event for the form is where you want to look into.
Adding to David's answer, you can make your email field optional and if they don't enter it the email will attempt to send but will fail and remain in your email queue until you clean it out.
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