This sounds like you are talking about 'compacting'. Q: Is this a pop or imap mail account?

When you delete emails, they are 'marked as deleted' and hidden from view. You may see them appear in the 'Trash'. The emails are still in the original folder, this helps to recover emails if deleted in error.

These 'marked as deleted' emails are using space and 'compacting' removes them.

Emails are stored in mbox text files. They are written one after the other in the order downloaded.

In trying to explain, think of it as one document with parargraphs = emails. Each one is like a paragraph in a document, so you would have various 'paragraphs' marked as deleted.

If the Inbox file has become corrupted in some way, then it may not know where the 'marked as deleted emails start or stop. Thus resulting in a loss of emails.

This is why you should not use the incoming Inbox as a store for emails. Create folders and organise emails. You should also compact the 'Inbox' and the 'Junk' more freqently to help maintain a heathier Thunderbird.

re :This hapens some month ago a first time, but after an restart of Thunderbird all messages are back again. But not this time. This would seem an indication of file corruption. It would have been a good idea at that time to get all good emails out of Inbox into other folders, delete unwanted emails, then when Inbox was empty, right click on Inbox folder and select 'Compact'.

If you want to use the auto compacting , I suggest you lower the threshold. If you want to stop auto compacting and use manual compacting then uncheck the option.

• 'Menu icon' > 'Options' > 'Options' >Advanced' > 'Network & Disc space' tab

If you want to stop auto compacting and use manual compacting then uncheck the option, otherwise: select: 'Compact all folders when it will save over XX MB in total.' Suggest you lower the XX MB to eg: 10 force more frequent compacting. click on OK

IF you are using a IMAP account, there are additional settings: Right click on imap mail account in Folder Pane and select 'Settings' Select 'Server Settings' Bottom right : select 'Clean up ("Expunge") Inbox on Exit' and it will compact the Inbox folder when you exit Thunderbird. If you check "Empty Trash on Exit" it will also empty and compact the Trash folder when you exit.

More info on compacting: what it does and why it is important.

• http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders

How to keep a healthy Thunderbird:

• http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

Q: Do you have a backup of profile name folder? Q: When performing a search for emails, have you ever used the Windows Explorer search method?

Please keep responses in the actual question. I've had to locate your profile to locate this question.

This is a copy paste of your response, so anyone helping in the forum can read it.

Thanks for your detailed answer, yes i mean compacting, i am a german and missing sometimes words in english.. i have an POP account. The Trash has no additional messages, even though junk or sent... Newer received mails are now in the inbox. I clean the junk-folder nearly day by day because it is so much.. You are right, i should make more or better organization but the child is now in the well.. So where may i find the "folder.?" I let Windows search for files with folder inside the name, but there is only 1 file, which belongs to Windows itself..

I never ever used Windows for mail-searching..

Regads Tomelle

How to check to see if there are any emails in the following locations: Do you choose to leave copies of messages on server ? In Thunderbird

• Right click on pop mail account in left Folder Pane and select 'Settings'
• Select 'Server settings' for pop mail account
• Q: Is this selected ? 'Leave messages on server'

If yes:

• please logon to your webmail account using a browser.
• Tell me if you have a load of emails, new and old in webmail account.
• Confirm, they are in the webmail 'Inbox' folder.

Make hidden files and folders visible:

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

In Thunderbird

• 'Help' > 'Troubleshooting Information'
• click on 'Open Folder' button

Window should open showing contents of your profile name folder.

• Exit Thunderbird now.

• Click on 'Mail' folder

You will see a list of folders; they are mail account folders. One will be 'Local Folders'. If you see only one other, this will be your pop mail account name folder. If you see two pop mail accounts with same name, but one has an additional number on the end, this implies that either you have two pop mail accounts using same server but different email addresses or Thunderbird lost track of one and created a second. What do you see ? You could post an image if it helps.

• Click on pop mail account name folder(s).

You should see: 'Inbox' and 'Inbox.msf', 'Sent', 'Sent.msf' etc Tell me if you see any folder with a .mozmsg extension. eg: 'Inbox.mozmsg'

mbox files have no extension. mbox files contain emails. mbox files can be opened using a text editor eg: Notepad

• open 'Inbox' file

Emails are written one after the other in the order downloaded. So the oldest will be at the top. Each email will start with lines like this:

• From - Sat Jan 24 06:49:35 2015
• X-Account-Key: account1
• X-UIDL: AIZUfbwAAAe8VMMp6QAAAIdKVu8
• X-Mozilla-Status: 0005
• X-Mozilla-Status2: 00000000

Q: Do you see only the new emails ?

If there are two pop mail account names, please check the 'Inbox' in the other account. please tell me if there are two and whether one of them has older emails in it.