re :''I keep getting the question about compacting my folders and when doing so a number of mails get erased.'' When you delete an email, it gets marked as deleted and hidden. Assuming you have gmail Account Settings > Server Setting When I delete a message: selected: 'Move it to this folder' and you have selected the gmail Trash folder. It should appear in the gmail 'Trash' and periodically gmail auto empties the Trash folder and removes email from the 'All Mail' folder where all emails are stored. If you have selected: 'Just mark it as deleted' then the email is not moved, it remains visible with a line through it. Gmail has not detected it is Trash, so when email is visibly removed by compacting the folder, only the label is removed and email is still on server in 'All Mail' folder as gmail has archived the email. Either way, the email is not fully removed from the 'Inbox' folder until you compact the folder eg: Inbox. Compacting removes 'marked as deleted' emails whether they are put into Trash or marked with a line through it. If you are discovering 'good' emails are being 'deleted': First check to see if the index is out of synch: Right click on Inbox and selct 'Properties' click on 'Repair folder' click on 'OK' If good emails are still gone, then you probably have a corrupted folder. For some reason Thunderbird cannot detect correctly where a 'marked as deleted' starts and ends. This can occur if you are not compacting as frequently as needed or perhaps the file has been 'fixed' by an Anti-Virus' product and they have messed something up. In this case, move all emails out of Inbox into other suitable folders. Delete anything you do not want. When Inbox is empty, right click on Inbox and select 'Compact. This will give you a nice clean Inbox file. If you have an Anti-Virus product, I would recommend you do not allow it to scan Thunderbird folders not scan incoming/outgoing emails. You can change the level when auto compacting requests, but increasing it will force fewer compact requests. It is better to compact more frequently than less especially if you delete a lot of emails. It is located here: 'Menu icon' > 'Options' > Advanced > 'Network & Disc Space' 'compact folders when it will save over XX MB. click on OK