How to make a subscription form for the site?

Question

User interface

I want to make a subscription form for e-mail newsletter on the site.
That's what I'm curious about. If the user specifies an e-mail that is already signed, then what should be done in this case? It should be taken into account that the target audience are women 40-60 years old, who may be at odds with the computer.

Options:
1. Do nothing. Just notify the user that he received an email with a link (well, as usual) and send a confirmation letter.
2. Report that such an e-mail has already been signed (I'm not sure if this is correct, including from the point of view of the law, because in this way I can compromise someone else's e-mail).
3. Report that the e-mail is incorrect. But here the user may have questions if he simply forgot that he had already signed up and indicates an already signed e-mail.

What would be the best way? And how is this usually done?

Answer 1

In your case, exactly var. 1. In general, I think 80% use this option as the easiest to develop.
About, 2 and the law - there are steps of confirmations.
3 is more for reg and other complex actions. Not "indicated incorrectly", but "already signed", incorrect - this is if you did not put a full stop.
Then work begins with interest - if the mailing is periodic and useful, then the user will no longer pay attention to the block with the form.