I have tried various approaches with this and keep coming up empty. Most times the user when trying to accept the suggestion gets a message indicating that the email they want to change to doesn't work because it already exists, which is not the case at all.
Anyone have any luck with this? Seems.... very unhelpful. Documentation on managed users on Atlassian doesn't seem accurate or up to date either. It states "Enter the new Email address and click Save changes." when I don't even have that option - all I can do is "suggest changes" at which point an email is sent to the user.