I'm using Thunderbird 58.0b3 on Windows 10 Pro 64-bit. I have a Gmail account with the following approximate numbers of messages: Total messages in All Mail (excluding chats): 26200 Messages with no labels: 15100 Messages with labels: 11100 Above, "messages with labels" means messages that have one or more user labels or are in one of the Gmail special labels (i.e., inbox, starred, drafts). I have Thunderbird configured to use Maildir, and I have set all folders for offline use except Sent Mail and Trash (also, Chats is neither subscribed nor downloaded). In the UI, when I click on each folder, Thunderbird reports the exact correct number of messages (as compared with the numbers shown in Gmail with conversation view disabled). According to the Thunderbird Gmail help page, Thunderbird downloads each message only once, even if it has one or more user labels -- so even though a message may appear in All Mail and in one or more labels, there should only be one copy of the message saved. Perhaps that was in reference to the mbox configuration only, because with Maildir, Thunderbird is clearly downloading the same message multiple times. The odd behavior I am observing, though, is that in the All Mail folder on the filesystem, and in the folders of some of the other labels, some of the .eml files appear to be missing. For example, the /[Gmail].sbd/All Mail/cur/ folder contains only 25,100 files, not the full 26,200 expected. If Thunderbird is not supposed to download duplicates, I would expect only 15,100 files in the All Mail folder, with the remaining 11,100 files divided among the folders of the various labels (in fact, in the folders of all the labels, there are over 11,100 total files saved). If Thunderbird does download duplicates for All Mail and each label, then I would expect 26,200 files in All Mail. Is it expected that there should be some intermediate number of files, somewhere between 15,100 and 26,200? Note, I have a second Gmail account with 6147 messages in All Mail, and the All Mail folder does indeed include all 6147 messages (even though most messages also have labels and therefore have duplicate files in the respective label folders). So, when using Maildir, is Thunderbird supposed to be downloading duplicates of Gmail messages? And if so, why is it failing to download all the duplicates?