Getting email addresses for users that comes from portal

Hi. My plugin listens to the URL /issueUpdated and looks at the req.body.issue.fields.reporter.emailAddress field. If reporter is a regular Jira user, then I can get his email if he has it open in his privacy settings (https://id.atlassian.com/manage-profile/profile-and-visibility).
But if the user created a ticket through the portal, then he doesn’t have privacy settings for email. In this case, the req.body.issue.fields.reporter.emailAddress field is undefined.
Do I need to add Oauth 2 to my plugin? Will this help?
Are there other ways to get an email for users from the portal?