What anti virus are you using. disk space errors when there is clearly an abundance are usually the result of contention issues. The most common cause of contention issues are anti virus programs scanning things that they should not. (your send file in this case)

Using G-Data antivirus, it never caused any problems. Thunderbird did save copies from sent e-mails, but just stopped doing that from one day to another.

Is this an imap or pop mail account?

'Menu icon' > 'Options' > 'Layout' > select 'Folder Pane columns' Enable the 'Size' column - see image below. What size is shown for the problem 'Sent' folder?

Do you need to save every copy of sent emails in that Sent folder? Have you ever deleted any emails from that Sent folder?

This is a pop mail account. Sent folder does not have a size, guessing that means zero Never deleted anything from this folder, it won't let me save anything in that folder. Beginning to think there is something missing.

Confirm what you have in Account Settings: right click on mail account name in Folder pane and select 'Settings' click on 'Copies & Folders' for the pop mail account Confirm you have these settings:

• Select: 'Place a copy in'
• Select: 'Sent folder on': correct pop mail account name
• click on 'OK'

Q: As you use a POP mail account, do you use a Global Inbox eg: Local Folders to recieve all incoming mail? So there are no actual pop mail accounts in Folder Pane only 'Local Folders'? If yes, then select the 'Sent' folder on Local Folders.

Confirm settings are all ok. Confirm if using Global Inbox Local Folders or actual pop mail account.

Those are the settings used for the pop account. Thank you for trying to help me fix this, so far no luck.

Please check the following.

Make hidden files and folders visible:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

In Thunderbird

• 'Help' > 'Troubleshooting Information'
• click on 'Show folder' button

a new window opens showing the contents of your Profile name folder.

• Close Thunderbird now - this is important

• Click on 'Mail' folder
• Click on pop mail account name

'Sent' (no extension) file is the mbox file that should be receiving/storing emails. Now check Attributes and Permissions.

• Right click on 'Sent' file and select 'Properties'
• On 'General' tab - at the bottom you should see 'Attributes'
• The 'Read only' and the 'Hidden' checkboxes should Not be selected - uncheck them if any are selected.
• click on 'Security' tab
• select your user name (assuming you have set up user accounts)
• Check the permissions. You need full control to 'Modify', 'Read', 'Write' etc, so make sure this is all allowed.
• click on OK when all is correct.

Now check contents of Sent file:

• Open 'Sent' file using 'Notepad'.

What do you see ? Is it completely blank or can you see emails? As the Size said nothing/zero, I'm expecting it to be empty, but please confirm. Emails are written one after the other in the order created, so the oldest will be at the top and each email starts with lines like the following:

• From - Sun Dec 28 18:14:40 2014
• X-Mozilla-Status: 0001
• X-Mozilla-Status2: 00800000

If there are emails, make sure each line which has X-Mozilla-Status: has the number 0001

• If you made any modifications, save the file.

• If the 'Sent' (no extension) file was completely empty, delete the 'Sent' no extension file.

• Delete the 'Sent.msf' file, this is an indexing file which Thunderbird uses to display what is in the 'Sent' mbox file. It does not contain any emails.

• Restart Thunderbird.

open Write and compose a short test email and Send to either yourself, or another email address you use or to a friend explaining it is just a test so ignore.

If you deleted both 'Sent' and 'Sent.msf' files, a new Sent folder should now appear in Folder Pane containing a copy of the email you sent.

Please confirm the following:

• Q: Did you need to uncheck any of the 'Attributes' ?
• Q: Did you need to modify the permissions on the 'Sent' file ?
• Q: Was the 'Sent' file empty?
• Q: Did the newly sent email appear in the 'Sent' folder in the Folder Pane?

Thank you, this solved the problem :-)

Attributes were set to read-only, unchecked that. Didn't have to change any of the permissions. Sent file was empty as you already suspected. New sent email was stored in the sent folder.

Good to hear that all is now working as expected.

As to the cause, I can think of two possible reasons, but it is highly likely to be the second one. 1. The 'Sent' folder had become corrupted possibly by a lack of maintainance and when it was compacted either manually or automatically, all mail was lost as Thunderbird could not detect the start and end of 'marked as deleted' emails. However, the changing of the 'Attributes' should not occur.

2. I would agree with Matt's comment. It is likely that the anti-virus product scanned the file and thought something was wrong, possibly performing a fix which basically deleted the original. Maybe the read only was created as a result of a temporary file whilst scanning due to AV. This does not necessarilly mean you had anything wrong - malware/virus - it could have just reacted on a False Positive scan result. Info on Anti-Virus:

• http://kb.mozillazine.org/Antivirus_software

I would advise you stop AV scanning any Thunderbird folder/file on startup. Also stop scanning incoming and outgoing mail.

If you start to find this 'read-only' issue occuring on other files and folders on your computer in general, then restart computer in Safe Mode and perform scans to make sure there is no malware/virus being a pain.

Possible reason could have been the compression part, since I do not allow my Av to scan incoming or outgoing emails. Lasts one: it takes too long to sent any email while scanning it :-)

Thank you all for your help, you are great people to help anyone with problems with Thunderbird.

Really hoping the question and its answers will stay on this forum, so they might help other people with the same problem.

Read only was only found in Thunderbird sent file, where ofcourse it shouldn't have been! Will keep this in mind.

Thank you so much again for your help :-)