What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I checked and indeed the button to add custom email address becomes disabled when you try to add an email that ends with .store.
I will send a request to our developers to allow adding ending with .store domain extension as a custom email sender. We will let you know once it is implemented.