Occasionally you will find duplicate user accounts when adding reporters, request participants, or watchers to an issue in Jira.
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Duplicate accounts
In the example below, the first, second, and fourth user in the dropdown list are all the same person. The first one is a licensed Atlassian user created by an Atlassian administrator, the second one was provisioned by Sailpoint as a Jira Service Desk Customer, and the third one was likely generated by interacting with Jira Service Desk by email with the michele.bromley@pdx.edu alias.
Which account should I use?
The assignee field in Jira only lets you assign licensed Atlassian users, but when adding reporters, request participants, or watchers, you will see all possible account types. If a user has an Atlassian account, you should use it whenever possible. This account will likely be the first in the list, and generally will have a profile picture.