+++ This bug was initially created as a clone of Bug #1110577 +++ This is spin-off of Bug 1106225 Comment 2. Phantom mail(messageKey=sizeOndisk, messageSize=0, no subject, 1970/01/01) is generated, if move from local folder to local folder, and if move fails because mail is deleted by other one while moving. [Steps to reproduce : Utilize Bug 1106225] (1) At local folder, Search, Select multiple mails, "Move To" to local mail folder. move target folder = Local Folder/Parent/FolderX => CopyMessage is requested "target folder depth" times(Bug 1106225) (3) When DoCopy for CopyService request #N is executed, mail in move source folder(Searched IMAP mbox) is already deleted by DoCopy for CopyService request #1. So, error in DoCopy #N occurs. => Because error while "local to local move", a phantom mail is created upon first error. => Because Offset of phantom mail is always sizeOnDisk. messageKey=messageOffset=sizeOnDisk && messageSize=0 is used, so msgDBHdr for phantom mail is re-used by all subsequent phantom mails. Then one phantom mail only isobserved.

[Steps to reproduce #2: Utilize spec of <menupopup type="folder">] has been found. See Bug 1106225 Comment 23.

Are there good theories of what conditions/bugs cause failure of DoCopy that can fix this (and the uplevel bugs)?

I can't think of a reason off my head right now. But I will re-visit this again in a few days, and so put another needinfo to myself.

[New simple Steps to reproduce problem] (1) Create Toolbbar button for test. (1-1) Install "Custom Buttons" addon, and create a Toolbar button using the addon. (1-2) Copy attached script to the created Toolbar button. (if you want to change number of phantom mails, please change loop count.) (2) Create local mail folder named "Test", "Test/S1" under "Local Folders". (it's hard coded in script. if you use other folder, please modify a var in script.) Thread pane column : Order Received, Date, Size (3) Create Virtual Folder(Search Folder). Search Target folders : some local mail folders which are appropriate for your testing. Condition : Subject doesn't contain !!!!! (=> all mails hits) Thread pane column : Order Received, Date, Size, Location (Account if required) (4) At the Virtual Folder(Search Folder) (4-1) Select some mails at Thread pane, (4-2) Add tag(eg. Important) to the selected mails for ease of observation(not mandatory). (4-3) Click Toolbar button created at step (1), with keeping the Virtual Folder selected, with keeping the mails are selected. (5) Check Local Folders, Test/S1 => Many phantom mails are generated. => Selected mails at step (4-1) are normally moved. => No dup mails is generated if Thunderbird 45 or newer. (6) At Test/S1, do clean up work for next test. (6-1) Move a non-phantom mail in Test/S1 to a local mail folder, in order to invoke Compact. (6-2) Compact => phantom mails disappear. messageKey(Order Received) is unchanged. (6-3) Folder Properties, Repair Folder => messageKey(Order Received) is re-assigned from 1. (7) Go to step (4) Note-1: If step (4) is done at Real Folder(non Virtual Folder, non Search Folder), phantom mail at move target folder couldn't be observed in my tests. Note-2: If move source folder and/or move target folder at step (4) is IMAP folder, phenomenon is different, because mechanism of "move mails" in IMAP is different from "move mails between local mail folders".