Add a jira-cloud-for-outlook label or "Issue created from Jira Cloud for Outlook" to the description when the issue was created or email was sent to issue from Outlook. This is for more insights or reporting purposes.

Workaround

This JQL will show issues with attached emails but won't show issues that were created from Jira Cloud for Outlook add-in and without the "Include email" checkbox ticked.

issue.property["atlassian-outlook-integration"].hasAttachedEmails > 0