Does it work with Google Assistant and Spotify?
You can use Speaking Email in conjunction with Google Assistant by long-pressing the action button on your headset, or equivalent bluetooth action button on your steering wheel if your car is linked to your phone via bluetooth. If you are using other audio apps, like Spotify, you need to pause the audio (click action button on headset), then launch Speaking Email (can use Google Assistant to do this), and then start listening to emails and interacting with Speaking email using your voice only. When driving, you can talk to your phone, as your would talk to a passenger in the car with you, but don't look at it or touch your phone if you can avoid it, as that could distract you while driving. Here is a scenario:
While I'm driving, I quite often press and hold the 'action' button on my headset to launch Google assistant, then say 'open Spotify', since my phone is in a car phone cradle on the dash board, I can then press the 'play' icon once Spotify is open, to get some music playing. I also do this for audiobooks (using MortPlayer).
If you want to interact with Speaking Email while the audio is playing from any source, you need to pause the audio (Speaking Email will not pause currently playing audio), so you can click (short press) the 'action' button on the headset to pause whatever is playing, then press and hold (long press) the 'action' button on the headset, and say 'open Speaking Email'. This will launch Speaking Email, and then start auto-playing new emails if you have auto-play setup in the settings. When you are done listening to email, or say 'quit' or 'stop' while the actions screen is open in Speaking Email, between messages, you can then click (short press) the 'action' button on the headset to resume music playing from the previous audio source, such as Spotify or an audio book reader like MortPlayer.
It sounds a bit complicated, but it is easy to get used to - again, make sure you try it before you start driving, so you are not experimenting while in traffic!