Compacting folders - Potential complications

__TOC__ Occasionally, when a folder is compacted the mail in the folder appears to disappear. In some cases there is a recoverable interruption or failure to display messages or message lists, and in some cases there may be real data loss. Some of the observed behaviours are below. Please review the items below and if you are still having difficulty please [https://support.mozilla.org/en-US/questions/new/thunderbird/form post your issue in support]. ==Selecting a folder while compact is in progress== Thunderbird can not read the index for the file while compacting is in progress, so when select a folder the mail in the folder will simply not be displayed until the compact completes. When the compact completes the mail will reappear. ==Software interuption to the process== Sometimes after the compact no messages display in the folder due to an interruption of the compact process. This causes an empty index (.msf file) to be created. Some possible causes of interruption and mitigations are: controlling or not allowing access to the Thunderbird profile folder for backup scans, cloud syncing (which is not recommended), or [https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues antivirus software scans] (which is not recommended). Right clicking the folder, selecting properties and then the repair button will force a new index to be built and should recover from this situation without data loss. ==Mail file has previously been deleted== Compact occurs and displays mail since the deletion. so the missing mail is all before a certain point in time. Whilst there have not need know instances in the recent past, historically anti virus products regularly scanned the mail storage file and is malware was found deleted or quarantined the file. Due to Thunderbird using an index to fill the user interface these types of deletions really only become obvious if an old mail is selected or a complete reindex occurs as in a compect process. ==File Corruption.== If the underlying MBOX file is corrupt, then the compact will write a new MBOX file that can at best be described as truncated. Often in this circumsatance the mail list retains the earliest entries, but later ones are lost from the point where the MBOX file became corrupt. Some of the more common causes are: hard disk failure, memory failure, software/ Malware corrupting memory where the data to be written to file is stored. ===Other symptoms of corruption in the mail store=== * Previously deleted messages reappearing * Messages with the date of 1969 * Message bodies containing bits of other messages * Messages in the message list not matching what is displayed when clicked * Thunderbird apparently going off to sleep before messages in a folder are displayed

Occasionally, when a folder is compacted the mail in the folder appears to disappear. In some cases there is a recoverable interruption or failure to display messages or message lists, and in some cases there may be real data loss. Some of the observed behaviours are below. Please review the items below and if you are still having difficulty please post your issue in support.

Selecting a folder while compact is in progress

Thunderbird can not read the index for the file while compacting is in progress, so when select a folder the mail in the folder will simply not be displayed until the compact completes. When the compact completes the mail will reappear.

Software interuption to the process

Sometimes after the compact no messages display in the folder due to an interruption of the compact process. This causes an empty index (.msf file) to be created. Some possible causes of interruption and mitigations are: controlling or not allowing access to the Thunderbird profile folder for backup scans, cloud syncing (which is not recommended), or antivirus software scans (which is not recommended). Right clicking the folder, selecting properties and then the repair button will force a new index to be built and should recover from this situation without data loss.

Mail file has previously been deleted

Compact occurs and displays mail since the deletion. so the missing mail is all before a certain point in time. Whilst there have not need know instances in the recent past, historically anti virus products regularly scanned the mail storage file and is malware was found deleted or quarantined the file. Due to Thunderbird using an index to fill the user interface these types of deletions really only become obvious if an old mail is selected or a complete reindex occurs as in a compect process.

File Corruption.

If the underlying MBOX file is corrupt, then the compact will write a new MBOX file that can at best be described as truncated. Often in this circumsatance the mail list retains the earliest entries, but later ones are lost from the point where the MBOX file became corrupt. Some of the more common causes are: hard disk failure, memory failure, software/ Malware corrupting memory where the data to be written to file is stored.

Other symptoms of corruption in the mail store

• Previously deleted messages reappearing
• Messages with the date of 1969
• Message bodies containing bits of other messages
• Messages in the message list not matching what is displayed when clicked
• Thunderbird apparently going off to sleep before messages in a folder are displayed