Is this for a POP mail account? Are the emails definately redownloading from server or are they old deleted emails that are being resurrected ? Menu Icon > 'Activity Manager' will tell you the number of emails downloaded, so if it says 10 downloaded, but you see 20 new unread emails of which 10 really are new. Then the extra 10 old emails were not downloaded, but are reappearing. If they really are downloading............. You would need to delete the 'popstate.dat' file and then Thunderbird will create a new one. The downside is that it will download everything that is on your server again, but just once. To keep the already downloaded emails away from a new download of everything in your server Inbox and create a clean empty mbox file ready for download............ Please do this: * move all wanted emails out of the Inbox into other suitable folders for storage and organising. * Delete any emails you do not want. * Right click on Inbox and select 'compact' to remove all hidden marked as deleted emails. In Thunderbird * Help > Troubleshooting Information * Click on 'Open Folder' * A new window opens showing the contents of your profile name folder. * Exit Thunderbird now - this is important. * Click on 'Mail' folder * Click on pop mail account name folder * Delete the 'popstate.dat' file. Start Thunderbird. A new 'popstate.dat' will be created, but it has no idea what has been downloaded previously, so it will start to download whatever is still in the server Inbox. Let it complete this task. This should fix the popstate file so that it has an uncorrupted record of what has been downloaded. When downloading has completed, delete any emails you do not want. Then compact the Inbox again to clean it up.