You can synchronize your contact list made with one of the following plugins:

• Ninja Forms
• Contact Form 7
• Formidable Forms
• Gravity Forms
• Bloom
• WooCommerce

Jackmail also allows you to make request to an existing html database using POST request

When installing Jackmail, a step is asking you if you want to synchronize existing active forms plugins with Jackmail.
If the plugin is installed after Jackmail, a message will say that it is now synchronizable.