turn off all email scanning in AVG unless you want it to make things worse. All it is doing is slowing the process probably by a factor of 5 and in the process probably corrupting the files.

I basically do not recommend any email scanning from anti virus products. It is not as if the Text file that represent email can actually execute malware, even if it is present. It would take you opening an attachment at least for it to be a problem and at that point avg should have scanned the file in the system temp folder, irregardless of if it is email word or any other program writing temp files.

It is also quite possible that each write prompts another scan of the inbox file resulting in scans that take something like 10 minutes per GB sp all they really do is create file contention. Downloading 3.9 Gb of data plus overheads is not a time when you want an anti virus making things difficult.

In addition to what Matt said: A gigabyte size Inbox is a bad idea. Best practice is to keep Inbox as tidy as possible.

When anti-virus software is corrupting Thunderbird mail files, this often results in data loss. Then your best bet may be to restore messages from a recent backup, assuming you did create one in the first place. In case not, see https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

Thanks for the replies.

Stopping Thunderbird and restarting it resulted in Thunderbird downloading more email.

I have all the options for checking for new messages off. I have Allow antivirus clients to quarantine individual incoming messages off.

The first time I tried to use Thunderbird to download my inbox, those options were set.

INBOX file 5964916 KB INBOX.msf file 25202 KB 38986 messages

When I ran Repair Folder the above options were off.

INBOX file 5600256 KB INBOX.msf file 23676 KB 38990 messages

The number of messages agrees with Outlook. I had received four e-mails between the two downloads. As I mentioned earlier, the repair removed both files and started over.

I am VERY concerned that downloading from Outlook to Thunderbird twice gives files whose sizes are so different (especially that the second attempt is smaller). I don't ask much of software, but if I do the same thing twice, I do expect to get the same result. My original goal was to have a backup of my email.

Should I turn off the AVG email checker and do the whole thing again? My internet is not that fast, it will take six hours for the download. And no doubt the size of the INBOX and INBOX.msf files created will not correspond to either of the previous attempts.

Is there some way to verify that the files have been properly downloaded, short of doing the whole thing again?

Should I try repair again or just delete the old INBOX and INBOX.msf? Or should I do something else?

I was hoping to start backing up all my folders today, but at this point don't have a lot of trust that Thunderbird will manage to do it correctly. I'd first like to have some faith that I am getting my Inbox downloaded without errors.

I feel like I am not understanding something fundamental. I assumed IMAP would just copy everything down with no drama. Could I get some suggestions for my next step?

I also noticed that in Synchronization and Storage

Keep messages in all folders for this account on this computer is checked

This Outlook mailbox I am having trouble with was created by creating a new profile, so that I could have separate personal and business emails with their own address books.

The personal email I set up first. All that downloaded was the Inbox. So I went to Synchronization and Storage. Under Message Synchronizing, I chose Advanced and clicked on the folders that I wanted to store locally.

Then I created this second account. I tried to do the same thing. However, Synchronization and Storage->Message Synchronizing->Advanced only Inbox shows up. No other folders. Did I miss a step? As I said I was trying to get a backup made. But no folders!

Obviously, if I got to OWA, they are all there.

I solved half my problem. I did leave out a step. Right-click on the email account and from the menu choose "Subscribe." Then check every folder and sub-folder you want to back up. After that, go to synchronize and select the folders.

Sorry for not finding that myself sooner.

But I am still quite concerned I cannot seem to download my Inbox and get the same sized INBOX file on each attempt.

Some more follow-up. I have seen many reports of folders disappearing. What seems to work to resolve the problem is-

Go to Account Settings. Then Server Settings. Then Advanced... There is an option Show Only Subscribed Folders. Make sure it is not checked. Click OK.

Quit Thunderbird and start it again. Folders should show up.

Go to Account Settings. Then Synchronization and Storage. Then Advanced under Message Synchronizing...

I find that I have to have Keep messages in all folders for this account on this computer checked.

I also had to go into Advanced... and check all the folders to get the mail to download into my profile. Note- nothing was showing up here (no folders listed under Advanced) until I did the previous actions.

Others have commented in another post that Show Only Subscribed Folders being unchecked and Keep messages in all folders for this account on this computer checked are the defaults. I may have created some of these problems using the Subscribe option. Now that my folders aren't just disappearing, I am avoiding doing anything with Subscribe.

I also find odd behavior if I don't let the computer stay on long enough to do all the downloading in one shot (get for example Sent Messages and Sent Messages-1).