There is no inbox file in the file system, only an index as a MSF file, say inbox.msf. The data for all current mail is stored in the CUR folder under the account in the profile.

There is no inbox file in the file system, only an index as a MSF file, say inbox.msf. The data for all current mail is stored in the CUR folder under the account in the profile.

I should have said "INBOX folder", not "inbox file". Each message folder in Thunderbird is associated with a folder in the file system that holds a CUR and a TMP sub-folder. When I lost data, the INBOX folder with its CUR and TMP sub-folders disappeared.

Are you still using a MAC ? What version of Thunderbird are you using?

Have you got any Anti-Virus product on computer which is allowed to scan your Thunderbird profile folders and files ? Although that is usually more of an issue when using mbox files.

In computer Recycle bin, is there any 'INBOX' or 'CUR' folder which can be recovered? OR perhaps in Time Machine ?

re :When I lost data, the INBOX folder with its CUR and TMP sub-folders disappeared. The CUR, TMP (contents of INBOX ) would be missing if the 'INBOX' was not there.

It sounds odd that the 'INBOX' folder was missing. If you logon to webmail account - are the emails still on server in Inbox?

At this point there's not much info to say whether the missing 'INBOX' (and contents) folder has been caused by Thunderbird or something else.

re :using maildir as the message storage format

How did you set that up ? Did you remove account, then set up Settings > General - Indexing section - Message Store type for new accounts set as Maildir, then add the imap account again ?

Did you use a tool like RecoveryTools Thunderbird converter ?

Do you access the account/email address via any other method eg: another computer or phone etc ? For example, if you accessed account using phone and pop, it may have deleted emails of server on download. Or deleted emails via another imap account on another device? Or deleted emails off server directly via webmail?

Have you recently altered any setting in the 'Account Settings'? Such as : change a setting in 'Account Settings' > 'Synchronisation & Storage' - 'Advanced' eg: unchecked INBOX folder

OR anything under 'Disc Space' ? eg: Delete messages more than x days old' ?

We could do with knowing what Account Settings you have got selected and whether anything was altered prior to the loss of INBOX.

Did you use 'Offline' mode before you discovered the problem ?

Many thanks for your message, Toad-Hall.

Are you still using a MAC? What version of Thunderbird are you using?

A Mac with Thunderbird 140.10.0esr.

Have you got any Anti-Virus product on computer which is allowed to scan your Thunderbird profile folders and files?

Only XProtect, which Apple includes in the operating system.

In computer Recycle bin, is there any 'INBOX' or 'CUR' folder which can be recovered? OR perhaps in Time Machine ?

An INBOX folder with cur and tmp sub-folders is in the trash. Either it wasn't there when I first had this problem or I overlooked it. I restored INBOX from a Time Machine back-up.

After I restored the folder, I repaired the folder again because some messages were still not shown. The same problem happened again.

Repeating the problem should have put a second INBOX folder in the trash. But there is only one. I don't know why.

re :When I lost data, the INBOX folder with its CUR and TMP sub-folders disappeared. The CUR, TMP (contents of INBOX ) would be missing if the 'INBOX' was not there.

Yup. I think that we're saying the same thing unless I'm missing your point.

It sounds odd that the 'INBOX' folder was missing. If you logon to webmail account - are the emails still on server in Inbox?

Seemed odd to me too.

All the messages in the inbox were still on the server and in other e-mail clients. I lost them only in Thunderbird despite many attempts to get Thunderbird to sync with the server.

re :using maildir as the message storage format How did you set that up ? Did you remove account, then set up Settings > General - Indexing section - Message Store type for new accounts set as Maildir, then add the imap account again ?

I created a new profile and set the message store type in Settings. Then I added my account.

Did you use a tool like RecoveryTools Thunderbird converter ?

I am not familiar with that tool. I have not used any tools.

Do you access the account/email address via any other method eg: another computer or phone etc ? For example, if you accessed account using phone and pop, it may have deleted emails of server on download. Or deleted emails via another imap account on another device? Or deleted emails off server directly via webmail?

I do not use POP anywhere. I access the server from my phone and sometimes from other e-mail clients. Messages were not deleted or moved from them. All the inbox messages were still shown in them.

Have you recently altered any setting in the 'Account Settings'? Such as : change a setting in 'Account Settings' > 'Synchronisation & Storage' - 'Advanced' eg: unchecked INBOX folder OR anything under 'Disc Space' ? eg: Delete messages more than x days old' ? Did you use 'Offline' mode before you discovered the problem ?

"No" to all. I just perused all the settings to prompt my memory. I've had no reason to change any settings other than identities.

</blockquote> We could do with knowing what Account Settings you have got selected and whether anything was altered prior to the loss of INBOX. </blockquote>

Since I reproduced the problem by repairing the folder again, I'm confident that the problem was caused by the repair process. I just don't know if the storage format was a factor too. Other people on the forum have stated that all messages in a folder disappeared after they repaired a folder. Most or all of them probably use mbox.

But if you would like to know more settings, which?

IMAP and SMTP at Fastmail. No local junk filter. Synchronize everything. Delete nothing.

Hi Matt

Does this sound similar to a bug report you created some time ago: https://bugzilla.mozilla.org/show_bug.cgi?id=1512080

Sounds like comment 9

Hi Rick

Take a look at that bug report and see if it sounds very familiar.

Take a look at that bug report and see if it sounds very familiar.

I found that bug report after I had my problem. The combination of the similarity of symptoms and the status of "unresolved" after seven years reinforced my decisions to revert to mbox and not file my own report.

My symptoms are the same as Matt's: the whole inbox folder in the file system disappeared. That's different from what Gene reported in comment 9.

What happened next for me is different from what happened in Matt's case. Matt got the messages from the server. I could not get Thunderbird to access the server.

What happened next for me is also different from what happened in Gene's case. Re-starting Thunderbird did not return my messages. But I'm not sure that I tried re-starting Thunderbird before I restored the inbox folder from back-up. Probably, I did not.