I need to prepare landing page to accept cancellation of email subscription. In the LP, I will prepare email form to ask which email address should be canceled the subscription.
Is that possible to check if the email in the form is already in Marketo?
If the email address is not in Marketo, I want to show error message "Your email address is not registered in our system. Please check your email address again.".
You could enable the form auto complete feature in the web form so when users arrive to the landing page the email adress to unsubscribe is already there.
Oier has the easiest solution.
The other way is to use jquery, which you may want to do if this email sub is related to a paid product that might have other email addresses.