Hi Dominic Riccetti,
You cannot run actions in the API. So if actions are being used to populate something like an action result in the UI, and then that action result is used in the send email action, you cannot do that via the API. The MethodAPIActionSendMail function takes in the parameters specified and sends an email.
However the application you are building to use the API ,can call other functions, e.g. using MethodAPISelect_XMLV2 to retrieve your customer information so you have their email address, etc. So you should be able to retrieve the information you need beforehand to full populate the MethodAPIActionSendMail function call
Dave