Scriptrunner Listeners - Send a custom email

[Dominiek Van Laenen]

Hello colleagues,

I would like to send a mail in case one of the fields (multi - user picker) changes (preferably only to the new people in the field). 

We have Scriptrunner, so we should be able to use Listeners - Send a custom email. 

How can I set up a condition to compare the current value of a field with the value it had before?

I think I can manage setting up the email. 

Thanks!