Error message for "already submitted" in signup form

Question

Consider a simple email signup for reference.

Is it necessary to inform the user they've already submitted their email so long as the initial submission was a success and the server identifies and ignores any subsequent duplicate submissions?

When working with form validation, I try to keep it as simple as possible. After some thought, I'm not sure an error throwback is necessary for the user if their email address has already been successfully collected. I'm failing to see any downside to handling the duplicate submission properly on server side (i.e. marking it as a duplicate or ignoring it altogether), and giving the user a success message.

Answer 1

I think you're on to something. I would say that handling it server-side only and not alerting the user would be an acceptable way of handling it. However, some sort of feedback could be useful and personal as long as they don't feel penalized.

One option is to tailor your submission response to be a generic catch-all. For example, it could just say "You're on our mailing list!" or "You're all signed up!" on success regardless of if there's a duplicate. This is a simple and direct approach, and it wouldn't make them feel bad for making a mistake.

Another thing you could consider is just sending automated e-mail saying "Hey, you recently tried signing up, but we've already got you on our list.". From there you could give the user options to go to your site, unsubscribe, inform them that they'll be receiving information on something soon, or link them to entertaining cat GIFs. That all depends on the purpose of your mailing list. This route might encourage users to feel a personal connection with the brand, and instead of feeling penalized they may see that you're just trying to help.

I'll think about that some more. If I can think of any other options or scenarios I'll update this response.