Compacting it an important maintenance task. Despite its poor choice of naming, it removes messages that have been deleted. When you select a message and hit delete it only marks for deletion and hides it from view. Compacting removes it and frees the disk space. The fact that you lost messages when compacting indicates that you do not maintain your email folders and they got corrupted. Read this article on how to maintain your email.http://kb.mozillazine.org/Keep_it_working_(Thunderbird)

My problem with compacting is that the original message is compacted so much that i can't see what someone has written or esp my reply. this has caused me all sorts of problems since I started using Thunderbird years ago. And I DO maintain my folders. I've lost some VERY important emails to this. I don't care about disk space. I've got more than enough. The worst problem are the archives, which automatically delete once the year changes. I finally set them so they wouldn't do that...but it was sorta too late by then

Please read the linked article on compacting so you know what compacting does. It has nothing to do with compressing file size despite its poorly chosen name.

I did. So why is so much info lost when it supposedly compacts?

Compacting removes corrupted data and messages marked for deletion. Poor folder maintenance is the usual cause. Like the OP of this thread that never wants to Compact again. This is a good article to read.http://kb.mozillazine.org/Keep_it_working_(Thunderbird)

I have just got used to pressing the cancel button every time i delete emails. Its a nuisance but having lost a lot of emails last time i am not going to do that again.

Whether its right or wrong I just would like to know how to stop seeing that message

I am not going to instruct you on messing up your email. Sorry. Maybe someone else will.

Bottom line is maintain your folders and it is not an issue. I have never seen that message or lost messages when compacting folders. But I follow the Thunderbird recommended procedures.

Really? I lost hundreds and hundreds, not sure where they went to.

On the toolbar > Options> Advanced > network and Disk space. and turn off Automatic compact.

You will probably first notice missing mail next when you click on mail and it is simply not displayed. We see lots of that here as well. That is the same data loss, without the re-index that compaction brings about. A lits of mails that once existed.

If you have appeared to lose mail in the past, it is usually because at some time in the past. Prior to the compaction your anti virus program has deleted everything in a mutant attempt to destroy some invented risk.

The folk over at svmantec were totally unconcerned when I tried to address their destructive tendencies. The fact that clicking the allow Nortons to fix the problem deleted whole inboxes going back years to remove something that was totally inert was apparently Ok. And it must be! Their customers keep giving them money and posting laments year after year, or like you blame something else entirely.

For year people come here with three misconception. 1. Thunderbird regularly looses mails. I have used it almost 10 years and my housekeeping is rubbish. (some 18,000 mails in my inbox consuming some 2.3Gb of storage) I have never lost a mail unless I did something stupid first, and then only once or twice. It the past Thunderbird certainly had issues of folder over 4Gb in size and lost mails. that is no longer the case.

2. That compaction does something about compressing mail. It is not compression it is compaction. A nuclear explosion creates a compression wave that compacts loose items. Likewise compaction in Thunderbird takes a sparsely populated data file and places the messages closer together by removing the space the deleted messages used to occupy.

3. That their anti virus program is actually a worthwhile product. Most issues with mail, data loss and inexplicable restarts or programs and windows itself can be parked right out front of the anti virus vendors doors. This is why Microsoft are really trying to squeeze them out quietly and without any finger pointing. That would just create litigation. So we get Microsoft Security Essentials, then Windows Defender, now Microsoft Family protection. None of these are any better than the third party products, and often leave gaping holes. But they result from the fact that anti virus software gives Windows a bad name. Mac users no not suffer anything like the issues windows users do in connectivity, and it is not because OSX is any better really.

Thanks, that's all I wanted to know!!!!

Now when you loose data, do not come here looking for assistance in recovering it. You have chosen a path that will ensure it happens and when it does it will be irrevocable.

Matt said

Now when you loose data, do not come here looking for assistance in recovering it. You have chosen a path that will ensure it happens and when it does it will be irrevocable.

I did lose data that's why I don't want to do it again. Thanks for your unhelpful comment though.

You may consider it unhelpful. I consider it fair warning. Compacting did not loose your data. Regardless of what you think.

Matt, I'm sorry, I'm on arkayla side on this. I deleted a few thousand obsolete eBay emails and then compacted the folder. I didn't have nearly as many as you. Compaction reduced the folder to unread: 0, total: 0. There were about 7000 unread. If I knew it was possible I could have taken precaution. I understand that anti-virus software is to blame. I also understand that Mozilla according to what I'm reading in this thread knows there is problem and didn't take time to put a warning screen up. Instead they extolled the virtues of compaction with no hint of potential problems. In the future I will drag my deleted files to a new folder before I mark them deleted. Then I can compact that folder. I certainly won't be compacting any folders I still have active mail in them.

DavidSorge said

Compaction reduced the folder to unread: o, total: 0. There were about 7000 unread

What I do not see in this thread is that occasionally it is the index that goes to god. Right click and select properties and then the repair button to force a re-index.

Matt, I'm sorry, I'm on arkayla side on this. Mozilla according to what I'm reading in this thread knows there is problem and didn't take time to put a warning screen up.

Turning your device on exposes you to the risk the hard disk will spontaneously fail. Leaving it plugged in during an electrical storm will risk frying the entire device.

Should there be a warning sticker on the Cord, a flashing message when you turn on the power. Of course not. We are all aware of such risks. Should Mozilla be putting a message on Thunderbird that says "Use of Norton's Internet security suite will probably cause your mail to be lost becazsue they will silently delete is and not tell you they did it." I really do not think it would last out the litigation.

Personally If I were writing mail software I would simply refuse to install on devices with products from Symantec or McAfee installed. Good thing I do not represent anyone but myself hey.

But I digress, when should you be warned? To take a real world example, a business does a stock take and establishes they have 10,000 screws. They sell 5,000 screws so their computer says they still have 5,000. They do a new stock take and find they really only have 100. When did those 4,900 screws go missing? Where are they? When should the computer have warned them there was a problem?

This is exactly what is happening in this instance. Thunderbird is methodically adding and removing items from the index, it is also adding items to the underlying data store, But like in the shop, it is not aware someone stole those 4900 screws (emails) until a new stock take is done. (rebuilding the index)

Should Symantec warn you that installing their software means they will delete all your mail without advising you that what they are deleting is your mail? I think it would be the least a multi billion dollar consortium should do. But they don't.

Do Microsoft tell when you upgrade to Windows 10 that the data and settings they are automatically converting are only for Microsoft products, so your Thunderbird mail will just get lost in the move. No they don't.

Do CCleaner advise you when you install their product that they will delete certain settings files for Thunderbird to "protect your privacy. They do in their settings, but it is only after the consumer comes here that they find out what it really means.

Does avast email all their user to tell them they make Thunderbird almost unstable with their latest release, .

And just to be incredibly clear here. I am a truly sloppy mail housekeeper. I have a huge inbox, over 20Gb of assorted mail data over probably 25 different accounts in hundreds if not thousands of folders.

Thunderbird has been merrily doing it's thing here for around a decade and I have never lost a single thing through compaction. Nor have I ever lost any mail through the actions of an anti virus program. However I also never allow an anti virus program to automatically fix anything unless I know exactly what file it is proposing to act on. It is really infuriating when they delete or mangle your current documents in an inane attempt to fix something that was working until they fixed it.

I understand where you are coming from, but I just can not do anything.