I have also tried the Linux apt-get update and apt-get upgrade and then a reinstall early on without any change in recovering this lost feature. At this point after spending ten hours to just migrate Thunderbird from my old computer to the new, I am concerned about trying yet another reinstall. Though its supposively the same Thunderbird package, it was NOT a simple matter of moving the .thunderbird directory from on to the other. Firefox migrations using that approach worked costing me only a half-hour of time; Thunderbird is now passing ten hours and I am looking at alternatives!

And while I am at it since it seems related, my transfer via filter are also not working anymore. As a new install, I am starting with no message filters thus creating them all again. I open a message, see its junk, select to create a filter using the From, set to transfer it to my PerJunk mailbox, and then select to run the filter. In the past, it would transfer that email from where I was looking at it TO the PerJunk mailbox. Now it does nothing....just like the "move to" features no longer does any transferring. I can live with pressing the delete button 100 times each day; but, would be nice to have the old features working on the new system.

Seems I wrote too soon. There is another email transfer protocol, that of saving a message after sending it by transferring it to a "sent" mailbox. I set it so any message sent is automatically saved in the Local Folder's sent mailbox for later "move to" if appropriate to my twenty mailboxes. Now I get the message there is a network error and though sent it can not be saved to "sent" mailbox.

I enjoyed the early days of MSWindows where the installation selected either single or multi-user environment. Mine has always been single user; but, I am forced into muti-user by all the new setups. If this is a permission/access issue, I have full "administrator" permissions. I even tried to start up Thunderbird via the terminal with sudo thunderbird" only to be told Thunderbird can not be run from the root. So now there are four means of email transfers to another mailbox which do not work anymore....

Following the thread that this was the violation of the KIS principal with the forced implementation of multi-users, groups, permissions, etc. complexity in single user environments; I was able to finally clear up the problem. It was one of file permissions.

start up Terminal cd /home/{username}/.thunderbird sudo chmod -R 777 *

This eliminates any read/write/execute limitations on any files in the Thunderbird directory which has been the email transfer issue all along. Its not the only one wasting my twelve hours. One might even go further is trudge down the directory tree a bit further through the {user profile} like ...-release/ to the Mail/ where in are all the mailboxes and filters. I just did it for the whole TB directory so I would not be visited by another time waster in my single user situation.