Is this an outlook/msn/hotmail/live mail account. For reasons best known to Microsoft their mail service with POP mail is flaky at best.

Their IMAP service apparently works better.

Thanks for the reply! I am using a not very common private mailserver (mail.cw-net.de)... So do you think the problem is on the side of the mailserver?

popstate.dat keeps a record of what has previously been downloaded for that pop mail account. Deleting it would have erased all knowledge of previous downloads and so would auto download everything again, but only the once.

When you deleted it, Thunderbird needed to be closed otherwise it would not have deleted it. If Thunderbird was closed before deleting popstate.dat file, I think you might discover a new one was created, but you had not refreshed the window, so it still showed a previous state.

If there was a problem with the popstate.dat file then what you did would have fixed that issue. So, I think there is nothing wrong with the popste.dat file.

Another real possibility to consider is that you have a corrupted folder. The emails may not actually be being downloaded, but maybe they are deleted emails that are reappearing. Try this: Move all good emails out of that folder into another suitable folder for storage. Delete all emails you do not want. When the folder is empty.....right click on folder and select 'compact'.

usually do not need to empty a folder before compacting, but if there is any signs of a possible corrupted folder then it would be wise to do as stated above to make sure you do not lose emails. Please read info on compacting what it does and why it is important.

• http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders