There is an occasional problem with Thunderbird and imap mailboxes that can destroy your user experience, especially if you tend to navigate using the keyboard, but even with the mouse it can interrupt your work.
The problem occurs only with unselectable mailboxes. These mailboxes don’t contain any mail, instead they contain other mailboxes that may contain mail. Normal, unselectable mailboxes will open to reveal their contained mailboxes when you click on them with the mouse or by the arrow keys. Normal selectable mailboxes will open to reveal their mail when you click on them.
Sometimes, an unselectable mailbox will get into a state where if you click on it, Thunderbird will give you an error, “The current command did not succeed. The mail server responded: Mailbox isn’t selectable.” Then you have to click ok to get the message to go away so that you continue working.
The part of the error message after “responded:” is server dependent. I am using dovecot on Red Hat and FreeBSD, so if you have a different server that message might be more like “The current command did not succeed. The mail server responded: Can’t open mailboxname: not a selectable mailbox” (uw-imap) or something else entirely.
You don’t have to click to see this problem. Selectable mailboxes in Thunderbird are displayed in Roman type. Non-selectable mailboxes are displayed in grayed, italic type.
I don’t know what is happening, but I have found a fix in my case. It depends on having shell or ftp access to your mail server.
On my server there was a hidden file inside my mail directory, .subscriptions. (.mailboxlist on uw imap, I think.) That file listed all of the folders that I was subscribed to, but it only listed selectable mailboxes with the one exception, the folder that wasn’t italicized. I deleted that one line.
That wasn’t a sufficient fix though.
Then I had to delete my entire profile entry for that mail server on my laptop. This was in the Thunderbird Profile directory under ImapMail/my.mailserver.com. I also deleted the file my.mailserver.com.msf in the same directory for good measure, but I don’t know if that is necessary. I actually had two mailboxes that were displaying this problem. Deleting the files on the client did cause one mailbox to be correctly displayed as unselectable, but didn’t fix the other, so it might be that you could get away with only this change.
For the other mailbox, deleting the my.mailserver.com directory and the my.mailserver.com.msf file was not sufficient. Both the change to .subscriptions (on the mailserver) and the deletion of the my.mailserver.com directory and file were required and they had to be made in that order.
I’m not completely happy with this solution because I don’t know how it broke, or why it this fix works, but there you go. The error/corruption/whatever you call it seems to happen sporadically. When I originally installed Thunderbird on my laptop, all of the folder were correctly displayed, but first one and then the other folder changed from italicized to roman and unselectable to apparently selectable without my being aware that I had done anything.
If you don’t have shell access to your mail server, you might be able to download the .subscriptions file through ftp, edit it, and upload the new file through ftp. It depends on how your server account is set up. It may be that your ISP or IT department has set things up so that access to your mail directory is impossible. On the otherhand, you might be able to see the .subscriptions file directly in imap. Finally, you might be able to prevail on a sysadmin to help you out with this problem. It really is a pretty bad problem in terms of creating a difficult user experience.
Usual disclaimers: back up both your server and client files before trying this. It worked for me but may not work for you.
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