Perhaps you might benefit from looking at he account setting then. As a yahoo customer you are of course limited to what they will allow you to do, and I am guessing your are expecting immediate deletions. You will probably get them for a few emails, but not Thousands your deletion requests are queued up and processed usually one at a timer. It takes time for messages to rattle up and down on the slow consumer internet connections offered almost all over especially the up part of the equation as it is usually only a tenth of that advertised as the download speed. Commercial connections are symmetric, consumer ones are rarely like that. So are you holding the shift key to bypass the trash folder with your deletions? I guess not as your deletions are going to the trash folder, or it could be a limit imposed by Yahoo. I really do not user them any longer they are just so random in their changes and decision making. Do you have the account settings> Server settings such that the trash is emptied when you exit the program? Do you have the setting in Account settings > junk Settings to automatically delete junk mail after XX days? Like you could set it to one. Note this well. Thunderbird does not check the junk/Bulk folder or the trash/deleted folder by default unless you actually select it. So nothing in either folder is downloaded until you look at it and initiate a download from Yahoo. You might want everything gone immediately and you can have that. But just be aware there is no going back. Once you have it that way. One inadvertent click on delete may delete important mail irretrievably. It is for this reason developers err on the side of caution and leave things around to be recovered for a few days. No one is perfect and on one never makes a mistake so programs allow for the human factor.