We have custom user fields (ie 'Business Analyst', 'Developer', etc.) in JIRA, and we would like to be able to send an email to those users when they are assigned to one of those fields. I have looked over the JIRA wiki, and could not find a way to do this.
I know this is possible with the 'Issue Assigned' event, but in this case, the JIRA is not being assigned, since we are using custom fields.
Is this at all possible?
You should look at the JIRA Scripting Suite plugin --- you can easily do something like that, and in fact, they provide a sample script that shows you how to send a custom email (https://studio.plugins.atlassian.com/wiki/display/JSS/Scripting+Samples).
But you do have to catch two use cases --- as a post-function to a workflow transition and as a plain edit. This plugin allows you to do both of those. I typically just worry about handling those things at the point in the workflow in which those fields are required for the first time, and handle it in a post-function.
This plugin completely changed the power of JIRA for me. I can quickly change scripts on the fly without recompiling or restarting JIRA. You must check it out.