I have an Apple iMac running OS X 10.8.5 and Thunderbird 24.5.0. The computer is set up for 2 users - myself and my wife. I have Thunderbird set up for me with 3 email accounts, and my wife has 1 email account. We have been using Thunderbird for many months without major issues. Suddenly today when my wife sent an email via her Outlook (Hotmail) account, it came up with an error message saying that the message could not be sent. I investigated and found (by logging onto Outlook) that the message had indeed been sent and was showing up in the Outlook Sent folder, but not in the Thunderbird Sent folder. After trying several test messages (with the same result), it is apparent that my wife's Thunderbird account is misbehaving as described above. I then tried my own account and was able to send emails using my Outlook (Hotmail) account normally. The messages were saved in the Sent folder as expected. I have tried turning off the computer and starting again - no change - my Thunderbird setup works as it has done previously, but my wife's setup no longer works as previously. So it would appear that the program itself is ok, but there is something wrong with my wife's setup. I have examined the contents of both of our Profile Folders using Thunderbird's "Troubleshooting Information" to show each Profile Folder in Finder. When I drill down to the "pop3.live.com" folders, there is a difference between the contents of those folders. My "pop3.live.com" folder contains the expected document files for "Drafts", "Inbox", "Sent", "Trash", etc... I can open and inspect the contents of those folders. According to Finder, my wife's "pop3.live.com" folder contains Unix Executable files rather than document files (They all have the expected names, just not the expected file type, and I cannot open and inspect the contents of those folders). Could this explain the behaviour described above, and if so, how can it be fixed? If this is not the answer, could someone point me in the right direction?