how to create custom field with the user email adresses

[Ankuskum]

I want to create field to show all the users email id's in jira service desk.

[Chris Buzon]

If you're looking to expose the Agent's emails (like the people using service desk), you cannot, unless you manually add each email as an entry into a select-type field.

This is an intentional choice, due to privacy laws - info about the users is made difficult to see in these ways.