

If you copy a message to another folder, Gmail will still store only one message but apply both folder names as labels to it. Similarly, if you move a message to a folder in Thunderbird, Gmail will create a label with the folder name and assign it to the message. When you apply a label to a message in Gmail, Thunderbird creates a folder with the same name as the label and stores the message in that folder. In this implementation, Gmail labels become Thunderbird folders. Gmail uses a special implementation of IMAP. Subscribing to folders and synchronizing messages Understanding Gmail labels and Thunderbird folders The Archive options… button is disabled for Gmail accounts, as it is not necessary to define the archive granularity with Gmail. In order to be consistent with Gmail's behavior, Thunderbird archives your message in the All Mail folder, and not in an Archive folder as it does for other accounts (as described in the Archived Messages article). Gmail's particularities Archiving messages

After you provide your account information (real name, email address, password), Thunderbird will automatically configure your Gmail connection. The Mail Account Setup dialog is displayed. Next, select File > New > Existing Mail Account…. See Google's article on “less secure apps” for help. Double check that “Access for less secure apps” is enabled.
