Login Form - assign users with client ID's

Let me see if I can explain it correctly.

I have a form where the when the client signs up, he will inform his email and then will receive a client ID (unique ID) in his inbox.

I then have a separate form, where I will add some information and I want this specific client to receive an email with that information. Can I add to this separate form only a client ID (not include the email) and the client still receives an email?

What I'm trying to say is can I pull up the email information from the database based on the client ID-only on a new form?

No its not possible. You cant retrieve data from your submissions to use on your form. 

Also according to our terms of use, it is forbidden to create login forms. This is due to some users abusing the system.

"Phishing. You agree that Company may terminate your JotForm Service immediately if a form's purpose is found to be deceptively obtaining: sensitive credit card information, social security numbers, user login credentials, or other sensitive personal information. All these activities are considered as Phishing and any account along with the violating forms will be suspended immediately.

Collecting Sensitive Information. You may not use the JotForm to collect certain types of sensitive information, including but not limited to credit card information and any type of login credentials."