I'm assuming you have an imap mail account. Imap accounts are designed to display whatever is on server in the subscribed folders. Gmail uses PUSH if IDLE is supported and it means gmail will open connection and force the download to allow imap account to reflect up to date situation on server. ''re :I also find that whenever I open the Gmail Inbox, Thunderbird automatically connects to the sever. Is this correct?'' Yes. It is an imap folder, when you select to open it connects to server. Emails may be fully downloaded or only headers downloaded. If only headers then when you select to read email, it is retrieved from the server and temporarilly stored to faciliate viewing. Good info at this link which may explain various things regarding an imap account. * https://support.mozilla.org/en-US/kb/imap-synchronization Going into 'Offline' mode to read emails means Thundrebird has no internet connection and so gmail will not be able to push emails. You can easilly go to 'Offline' mode by clicking on the Offline/Online icon located far left in bottom 'Status bar' , same again for returning to 'Online' mode. You may also be interested in this: * Menu app icon > File > Offline > Download/sync now * Select checkbox: 'Mail Messages' * Select checkbox: 'Work Offline once download and/or synchronisation is complete' * the 'Select..' button offers you the opportunity to check all folders are selected for full copy download. * Once all set up click on 'OK' download.Sync occurs and then Thunderbird goes into Offline mode.