Are you highlighting an issue you have or a feature you'd like to see? The Android client is not designed to sync with your desktop client, it downloads emails from your mail providers server. Is your android client connecting to the server using Imap (prefered) or the pop3 protocol? '''Imap''' keeps your emails in sync with the server. To enable sync for one or more folder ... # Open the account list # Tap on the applicable account. # Tap manage folders (bottom of list). # Tap desired folder name. # Toggle "sync" to ON. # Repeat for each desired folder. '''Pop3''' was intended for use with only a single email client. It simply downloads a local copy of new emails and has no concept of folder sync. After an email downloads, it's typically deleted on the server. You can change how these deletions are managed through a combination of app and your providers webmail settings. To find these settings in Thunderbird for Android; Navigate to settings > account > fetching mail ... * When I delete a message (pick from options) * Erase deleted messages on server (pick from options)