You can do this two ways: with a custom plugin you create yourself or you can get the Email Expansion Kit add-on and define your emails as separate templates.
The Email Expansion Kit add-on was already setup on the website, but would this add-on work for sign-up notification that admin are receiving?
Yes, you can use the same trigger. You’ll probably want to disable the notifications in the main plugin.
I have 3 types of forms and each has email template that goes to volunteers email address. These email was setup to use one trigger which is called “Signup Submission Thanks”. So now I did use the Email Expansion Kit add-on to notify the admin. What I did is that I created 3 email to differentiate which sign-up was that for and I used the same trigger for all of them (which is still “Signup Submission Thanks”). Now, the admin is receiving 3 notification emails. How can I set it up so that I can tell what sign-up is that for? Do I have to define 3 different triggers?
You need to use “send on condition” for each template. Set them up to look at a value in the submission that indicates which form was used.