Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi SkyePerez,
Thank you for posting your issue on Microsoft Community forum. Yes, you are right conversation includes all messages in the same thread with the same subject line, Outlook shouldn't create a new conversation randomly for the same subject.
Which type of email account (e.g. Exchange Online/IMAP) and Outlook 365 version are you using, please provide us with the detailed version, see About Office: What version of Office am I using?
Does this issue happen with any other users in your organization?
However, I have searched but haven't found any way to manually modify the header data to put it back in the email conversation.
Moreover, please provide us with the detailed screenshot about the issue via the Private Message for further analysis.
Your patience and cooperation are highly appreciated.
Best regards,
Shyamal