Check tools>account settings>synchronization&storage. You may have it set to delete messages older than 14 days. I am not familiar with a way to recover deleted messages, but there may be others on this forum who can advise otherwise.

Thank you, David - I checked the settings but the account was not set to delete messages older than 14 days :(

When you move or delet an email, it is moved to the appropriate folder. In reality, the original is still in the original folder, but now it is hidden and 'marked as deleted' Compacting removes those hidden marked as deleted emails. More info: https://support.mozilla.org/en-US/kb/compacting-folders

However, if the folder had some corruption then it might explain why something went wrong. Corruption could occur if folders are not regulary compacted or if Anti-Virus scanned file and tried to fix it or if Thunderbird was still compacting folders when it was closed etc. https://support.mozilla.org/en-US/kb/compacting-folders-potential-complications

See if this issue is caused by a duff index file.

• Right click on folder and select 'Properties' and click on 'Repair Folder' - click on 'OK'
• Repeat for each folder.

As for recovery: Do you have any Nstmp files in the same location as the stored emails?

• Help > More TRoubleshooting Information
• Under 'Application Basics' - half way - Profile Folders - click on 'Open Folder'

A new window opens showing contents of your profile name folder.

• If pop account - click on 'Mail' folder and then click on the pop account name folder.
• If imap account - click on 'ImapMail' folder and then click on the imap account name folder.

Q: Do you see any Nstmp files with a good size? If yes:

• Exit Thunderbird now - this is important.

These nstmp files are temp files and normally get created during compacting and deleted after, but if you see any it means compacting got interrupted and they may contain emails. You can Open nstmp files using a text editor like Notepad++ Then you can see where they are emails you received or emails you sent. If you have those files then make a copy and rename it something like 'OldInbox' and save file. If it has an extension like OldInbox.txt then use rename to remove the extension. This will create a mbox file - note you may be asked if you are sure about doing it.

Alternatively - do you have a backup of your Thunderbird profile folder?

• C:/Users/Username/Appdata/Roaming/Thunderbird

Let me know and I can advise further.

Personally, I would advise it would be ideal if doing compacting on all folders, to go into 'Offline' mode first to prevent any server connectivity and then allow compacting to occur. I do not select any folder etc whilst compacting takes place. It usually is completed within a matter of seconds. I also do not allow the Anti-Virus any access to any Thunderbird profile files or folders.

Help to keep on top of compacting - eg: If imap -Set up Inbox to explunge on exit. This is in Account Settings > Server SEttings

Manually Compact the folders most likely to need more frequent compacting - Inbox, Drafts, Junk I have just got into the habit of manually compacting those folders at the end of each day. Do not store older read mail in the Inbox as that folder gets the most activity for receiving and deleting emails. Use other folders to organise and store emails for the reason that cuts down the risk of loss.