Thanks - I see that note now. As some messages had retained their new subjects I guess they were the ones I modified while they were still in New Mail. Now I know.

Seems I am having a small spate of problems.

Some 1400 emails in 1 folder and 300 or so in another (just some of my emails). The subjects in the emails were inconsistent and in many cases unclear - especially as Pmail clips overly long subjects. I spent many hours modifying the subjects via the email's properties. This so that I could sort the emails by date/time within subject. I then reindexed the folder only to find that all my changes had been undone. Now that really cheeses me off. Advice anyone?

Did you see the note at the bottom of the Properties window which reads "Changes in this screen may be lost or altered if the folder that contains the message is reindexed or otherwise modified."?

Editing the Subject or From field via the properties of of an email in a normal folder, but not in the New Mail "folder", only modifies the data in the index (.PMI) file for that folder. The data in the messages (.PMM) file is unchanged.

When you reindex, the old index file is completely recreated by parsing all the messages in the messages (.PMM) file so the Subject and From fields in the index file are duplicated (and possibly truncated) from the messages file.

Editing either of those fields of a message in the New mail "folder" modifies the header of that message by adding lines starting X-PMDFROM and X-PMDSUBJECT.
If that message is then moved into a normal folder then you can reindex the folder without loss of the new data.

Note that although the new data will appear in a folder window the original Subject and From fields are displayed in the message reader.