My first thought is to make sure that format emails is turned on
https://docs.vapi.ai/assistants/voice-formatting-plan#19-formatemails
Then have the bot repeat the email back to the user to make sure its correct. Then under analysis -> structured data (in the vapi assistant dashboard) you have have it output the email as a string. Alternatively you can have the transcript send via a webhook to something like make.com and have a GPT step, just feed it the transcript and tell it to exctract the name, email and whatever else and output it in a JSON format. Then it's easy to feed into google sheets or whatever else