Does anyone know how to find variable on Cards and Board?

Question

Does anyone know how to find variable on Cards and Board which is NOT on the list as shown below:

https://help.trello.com/article/1157-variables

for example: user's email address, email for this card

Arne Albers · Answer

Hey there,

I would also like to get the users email as a variable. To be able to send the user that triggered an action an email (via automation){usermail} does not work I guess.. Because it is not in the documentation.

Best wishes

Arne

Iain Dooley · Answer

@Shohei Mitsuhashi you can't get either of those things (either with Butler or with the API), but you can send an email to members of a card using Butler.

milynnus · Answer

@Shohei Mitsuhashi

I have tried and I am able to get my own email but not too sure about other board members because they were all empty. They were no errors. 
I was not successful with card email.