You can collect email addresses of potential clients or leads in the Google Form.
First, create a form with the fields required for your form. Do not create an email field.
See this demo for an example:
# Go to settings and enable collect email addresses option
Go to the settings by clicking on the 'settings' icon on the top right
Then select the collect email address option:
Google forms will add an Email field.
# Collect the email addresses to a Google Sheet
In the responses tab, click on the Google Sheets icon. now you can collect the form submission data to a Google Sheet.
When you want to send email to all the users in who submitted the form, just use the Rapid MailMerge add-on for Google Sheet to send personalized email to each user directly from the Google Sheet.