Moving messages between folders in a Hotmail-imap account in TBird results in deleting the content of the attachment. How it looks in TBird is that the mail message is still there, and you see the attachment, file names etc., however the size is unknown and downloading it results in an empty file, and there's a popup message, roughly paraphrased as the attachment is corrupt. On outlook.com, a popup message states a similar event, paraphrasing, 'Attachment cannot be downloaded etc.'). Is there any way to recover these files/attachments after the fact? As far as I can tell, this is irreversible and not amenable to Outlook.com's web interface "recover deleted messages" feature, as the message itself has not been deleted. I reproduced this in a new instance of Thunderbird (i.e. extension free, completely clean, only one account) and moved a single message, left TBird running for a while, and got the same result. Called up MSN support and as expected, fingers were pointed, the explanation/guess given to me on the phone was that this was due to a synchronization error, i.e. I didn't give Thunderbird the chance to synchronize properly with Hotmail (since I initially moved several messages at once). The above test debunked this, as only a single message was moved (preventing let's say a confusing cross command to neglect the first move and do the second), and additionally, just the attachments disappeared, not entire messages. However some attachments didn't disappear. I though this would be relevant to mention. Generally, compressed files disappeared, jpegs less likely. None of the attachments were super large of even came close to exceeding Hotmail's limits (otherwise I would not have been able to send/receive them in the first place). Most losses were in the kbyte range. For the same reason, I rule some internal Hotmail anti-virus incoming scanner, as generally attachments aren't stripped and they give you the option to 'trust sender' etc. To reproduce this, first of all, set up a dummy Hotmail account, make sure there is nothing important in there, connect that to TBird through imap (just setup new account and login, TBird will automatically detect the settings). Send a test message/with attachment to yourself (useing web or TBird). Then, in the Thunderbird program, drag the received message to any other folder in your dummy Hotmail account. Try opening the attachment after the move, in the new folder. TBird will return a popup saying something about the message being corrupted. From my point of view, this is a bug in both Thunderbird and Outlook.com, and a serious one, losing attachments is as awful as it gets, it's the very definition of data loss. To me it's not different than losing a file on your desktop, especially when experience has taught that the two most popular mail services, are as reliable as they come. I should note however, that I couldn't reproduce this problem in TBird-imap with Gmail, so google is seemingly immune. Nevertheless, someone should address this issue for connecting to Hotmail which is one of the most popular services. At this point in time, I will not touch any Hotmail account with TBird, my primary interest is in finding anyway to recover the troves of attachments I had already lost. I would appreciate any suggestions from anybody.