Hi Steven! You CAN do this using the merge tag for their email address, but I wouldn’t recommend it. This can lead to unpredictable issues with deliverability. You can leave the send from email as the site admin, but I’d really suggest using a third-party SMTP provider like SendGrid to send out those emails. Even beyond that, I would suggest that you set up a SUBDOMAIN to send the emails with that third-party sender. This means that the emails from your website might come from an email like “website@sg.companydomain.com”.
If the issue is that you would like to simply reply to the email and have it go to the user, then put the user’s submitted email address into the “reply to” field. For instance, the user submits a contact form and gives their email address, the email gets sent to you, and if the merge tag for the user’s email address was in the reply to box, you should only have to hit reply and the email will automatically get addressed to the user.
Sending an email notification from a domain other than your website’s domain is not a great idea and often a one-way ticket to the recipient’s SPAM or Junk folder. That’s if it reaches the email client at all.
If the idea is to display who filled in the form, why not display the name in the subject using merge tags? If you want replies to the notification to go to the person who submitted the form, you could add the email to the Reply To field using the Email field’s merge tag: