I am a very long time user of Outlook Client (Classic) mail app from MSFT. It has been my practice to annotate incoming mail by editing the subject. For example when I receive an email about a financial transaction such as a online payment or a charge, I edit the subject adding the amout, what was the charge/purchase for and sanitized last four of account number plus any other useful info. I move these emails to a separate folder, either "eBills" or "Receipts". That way I can quickly find receipts, bills, and other transactions without having to open each individual mail message. Apparently Thunderbird does not support this functionality. Is that correct? Thanks, Robert