it is useful to offer some info on what type of account you're talking about. '''POP''' Pop mail accounts only look at Inbox and download whatever has not been previously downloaded. They cannot access nor download from any other folder on the server. So if you do not want older emails downloading, then you need to access your webmail account using a browser and move all older emails into a suitable folder, but not the Inbox, then Thunderbird cannot see them. By default, it usually downloads and deletes the copy on the server, but you can change this preference. * Tools > Account Settings > Server Settings for the mail account or * menu icon > Options > Account Settings > Server Settings for the mail account select: 'leave messages on the server' optional: select: 'for at most xx days' this will delete anything older than specified number of days select 'Until I delete them' when you delete an email it will be deleted off the server. click on Ok to save settings. '''Stopping a download:''' There is a button you can add to the Mail toolbar. * View > Toolbars > customise or * Menu Icon > Options > Toolbar Layout Drag the 'Stop' icon onto toolbar. close Customise window - top right X. click on 'Stop' icon to stop current action of download. '''IMAP:''' IMAP mail accounts see a remote view of the subscribed folders on the server, so you would see whatever is in any subscribed folder. You can choose to synchronize subscribed folders and select settings to limit what is downloaded. Tools > Account Settings > synchronization & storage. see good info at this link: * https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage