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Outlook Express must keep a mark of which emails it has downloaded using POP3 protocol so that it wouldn't download them again in case downloaded emails do not get deleted on the mail server after they had been downloaded.

Where does OE keep this mark and is to possible to change it manually to trigger/suppress downloading of emails being on the mail server?

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up vote 4 down vote accepted

This file "Pop3uidl.dbx" file in your Identity's store folder keeps track of which messages on the server have already been downloaded. If you delete "Pop3uidl.dbx", the next time you check for mail, all the messages on the server will be downloaded again, and a new "Pop3uidl.dbx" will be created.

Should you wish to analyze the contents of this file, Arne Schloh has published his analysis of the dbx format here. But you may be able to short-circuit the search for these bytes, by copying Pop3uidl.dbx aside, downloading some messages, then doing a binary compare between the before and after copies of Pop3uidl.dbx. This might give you the byte offset of the information that you seek.

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It stores this information in the local copy of your mailbox, as it uses the message headers to determine if it has seen the message before.

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And as OE uses big files (with the horrible 2GB limit, and its need for compression after deleting messages) to store all this info, I doubt one can manually change that information. – Arjan Sep 23 '09 at 12:29
How do you know that it uses the message header to determine if it has seen the message before? – Piotr Dobrogost Sep 23 '09 at 12:45
@Arjan What do sizes of other dbx files have to do with this specific dbx file which isn't that big as far as I know? – Piotr Dobrogost Sep 23 '09 at 12:47
I think Arjan means the .PST file limit... after 2 gygs it gets corrupted... – Aaaaaaaaaha ERLEBNIS Sep 23 '09 at 13:44
@Piotr Because I wrote a POP3 server for my dissertation, and used Outlook express to test it ;) – Rowland Shaw Sep 23 '09 at 14:45

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