Need a form to send an email to a client, retrieving the email address from another form in another app

Need a form to send an email to a client, retrieving the email address from another form in another app

I have a form (call it formA) in an application (call it applicationA) in which I register all my clients service requests. And all the information of my clients are located on the client form (call ir formB) on a client database application (call it applicationB).
What I want to do is for the applicationA to execute an action, "on add" / "on success", that sends an email to the client with a confirmation of the service request registered on formA, using his email (the client´s) located on the client database, on formB, on applicationB.

Need to solve this ASAP... thanks