I have read through the answer to this question asked several different ways and still don't get it.

I think the problem for most people is the idea that "purge" means the same thing as "compact". In whose mind are these two words synonymous? Certainly not mine. "Purge" means get rid of, make go away; "compact" just means make smaller, squeeze together, clean out the gaps, etc. I think most of the people questioning are just trying to say they do not want there deleted messaged deleted -- read "purged" -- until they intentionally delete the deleted. If I wanted it immediately, automatically deleted, i.e., purged, from my disk, I wouldn't even need a trash folder.

Just correct the annoying message to say what it apparently means, "compact", NOT "purge".

billb1111 et al The problem has occurred because: most people have no idea what goes on within the mbox file when they delete or move a message. When you select to delete, a 'COPY' is put in the Trash and the original is still in the original file, just hidden and marked as deleted. As you mention : If I wanted it immediately, automatically deleted, i.e., purged, from my disk, I wouldn't even need a trash folder. This clearly shows that you do not understand what is going on when you delete a message.

When people see "The messages you have deleted", the general user believes this refers to messages they have deleted and are now being displayed in the 'Trash' and who would blame them because without knowledge of the background goings on in Thunderbird files, that is the only conclusion they would believe. So couple that with the words "can be purged from disk" and you can easily understand that people believe it means completely get rid of any message I have selected to be deleted...aka..Empty my Trash now.

In reality, any message that is moved or deleted from the 'Inbox' is still in the 'Inbox', but now it is hidden from view and has been 'marked as deleted'. The user does not see this and most do not know about it, so when the pop up asks about 'the messages you have deleted', it is talking about those 'hidden and marked as deleted' emails that still lurk in the original folder and not the list of copies of deleted email in the 'Trash' folder.

The "can be purged from disk" is now talking about looking for all those 'marked as deleted' emails in the original folders - not the copy in the 'Trash'. A copy of the mbox file is created and then those emails that were marked as deleted are removed. So compacting changes the actual data stored in the file - 'marked as deleted' emails have been purged. Compacting a folder frees wasted space but the main reason to do it regularly is because it's a type of preventative maintenance and when done frequently, it reduces the risk of corrupted files.

The pop up message may appear ambiguous as it uses different terminology from otherwise used in Thunderbird for Options setup for compacting and also in all Help and Support Articles. People do not seem to understand that 'compacting' is not 'compressing'. Compacting is purging; it is changing the data stored. It is completely removing old marked as deleted emails. It is purging them from the disk. It is making the mbox file smaller because data has been removed. So, technically there is nothing wrong with 'purge from disk', it is accurate. It's just that it causes confusion, when everyone has got used to the word 'compact' and when 'compact' is used in Thunderbird and used in all Help Articles. So using the word 'purge' is just not helpful.

Compacting is not compressing. Compressing is like zipping, the data uses a lossless compression formula which allows the original data to be perfectly reconstructed from the compressed data. It does not change the actual data stored - nothing is deleted nor purged. It keeps the same data but compresses it into a smaller file, which would need to be unzipped for access.

Helpful links. http://kb.mozillazine.org/Thunderbird_:_Tips_:_Compacting_Folders https://thunderbirdtweaks.blogspot.com/2011/07/compacting-what-is-it-and-why-must-i-do.html

Failure to compact folders on a frequent regular basis can end up with single text text document file of large size when a large proportion of that document is old messages you have deleted perhaps deleted a long time ago. The file could become corrupted with potentially bad results.

Please do not ignore this pop up that asks to purge old previously marked as deleted emails from their original files. The folders that usually need the most 'compacting' are Inbox, Drafts and Junk because those files get the most deleting and moving of emails.

I created a bug report, which is asking for the wording to be put back into a language that is used within Thunderbird 'Options/Preferences', that is used in all Help Articles. Basically use the words 'compact folders' to recover space. It would be helpful if others could actually vote for this bug report and help me get the attention of the developers. It would be perhaps one of the easiest fixes to do, but not so easy to persuade the powers that be that they got it wrong and it is causing alot of unncessary concern and wasting the time of helpers who need to explain everything repeatedly in several identical questions. https://bugzilla.mozilla.org/show_bug.cgi?id=1678856

Thanks, Toad Hall - I think I understand now!

Richard Davis