Please define "virtual folder".

Is this a Saved Search folder? And where does the .dat file appear? I don't think I've ever seen one of those in Thunderbird's profile, apart from the very specific files for message filter rules.

Yes, a Saved Search folder, I used the term "virtual folder" because the actual messages aren't stored in it. On Linux: "$HOME/.thunderbird/PROFILE/virtualFolders.dat", where PROFILE is whatever "Path" is listed in "$HOME/.thunderbird/profiles.ini"

@ Smokeytm: Could you tell us which version of Linux and which version of Thunderbird and how you installed it? I have Xubuntu 14.04 with Thunderbird 38.5.1. I have just created a 'virtual folder' (a saved search folder) with the name 'From: Jim' (in case the colon was causing the problem). I have closed and restarted Thunderbird and everything is fine, with no 'bogus' folder created. So I'm thinking that there must be something in your particular set-up that is causing this. @ Zenos: the 'virtualFolders.dat' file exists in my profile whether or not I have a saved search folder in the folder pane, so I assume it's a standard part of a Linux installation.

I'm going to ramble a bit.

I'm running Fedora 22 with latest updates using dnf distro-sync. The current kernel version is kernel-4.4.3-201.fc22.x86_64. The current thunderbird version is thunderbird-38.5.0-1.fc22.x86_64. I used the following command to list dependencies:

rpm -q --whatprovides $(rpm -q --requires thunderbird | sed -e 's/[[:space:]].*$//' | sort -u) | sort -u | sed -e '/no package provides rpmlib/d'

The list of installed dependencies is: alsa-lib-1.0.29-1.fc22.x86_64 atk-2.16.0-1.fc22.x86_64 bash-4.3.42-3.fc22.x86_64 cairo-1.14.2-1.fc22.x86_64 dbus-glib-0.104-1.fc22.x86_64 dbus-libs-1.8.20-1.fc22.x86_64 firefox-44.0.2-3.fc22.x86_64 fontconfig-2.11.94-4.fc22.x86_64 freetype-2.5.5-2.fc22.x86_64 freetype-freeworld-2.5.5-1.fc22.x86_64 gdk-pixbuf2-2.31.6-1.fc22.x86_64 glib2-2.44.1-2.fc22.x86_64 glibc-2.21-12.fc22.i686 glibc-2.21-12.fc22.x86_64 gtk2-2.24.29-1.fc22.x86_64 hunspell-1.3.3-5.fc22.x86_64 libffi-3.1-7.fc22.x86_64 libgcc-5.3.1-2.fc22.x86_64 libjpeg-turbo-1.4.0-2.fc22.x86_64 libstdc++-5.3.1-2.fc22.x86_64 libvpx-1.3.0-7.fc22.i686 libvpx-1.3.0-7.fc22.x86_64 libX11-1.6.3-1.fc22.x86_64 libXcomposite-0.4.4-6.fc22.x86_64 libXdamage-1.1.4-6.fc22.x86_64 libXext-1.3.3-2.fc22.x86_64 libXfixes-5.0.1-4.fc22.x86_64 libXrender-0.9.9-1.fc22.x86_64 libXt-1.1.4-10.fc22.x86_64 mozilla-filesystem-1.9-12.fc22.x86_64 nspr-4.11.0-1.fc22.i686 nspr-4.11.0-1.fc22.x86_64 nss-3.22.0-1.0.fc22.i686 nss-3.22.0-1.0.fc22.x86_64 nss-util-3.22.0-1.0.fc22.x86_64 pango-1.36.8-6.fc22.x86_64 sqlite-3.10.2-1.fc22.i686 sqlite-3.10.2-1.fc22.x86_64 startup-notification-0.12-9.fc22.x86_64 thunderbird-38.5.0-1.fc22.x86_64 xulrunner-38.0-1.fc22.x86_64 zlib-1.2.8-7.fc22.x86_64

I just created another Saved Search folder "From: mozilla.org", in the user interface it was listed correctly, on disk it was created as "From3e94fecf.msf" (e.g. "$HOME/.thunderbird/PROFILE/ImapMail/mail.example.com/From3e94fecf.msf"), within the "From3e94fecf.msf" file is this entry: "(83=From: mozilla.org)", and within the "virtualFolders.dat" file there is this entry:

uri=imap://rag%40example.com@mail.example.com/From%3A%20mozilla.org scope=imap://rag%40example.com@mail.example.com/INBOX terms=AND (from,ends with,mozilla.org) searchOnline=false

Other than the name of the file on disk everything seemed OK. But, when I close thunderbird and re-open thunderbird, I see both "From: mozilla.org" and "From3e94fecf" virtual folders. On disk there is still only one file "From3e94fecf.msf", but, in virtualFolders.dat, I now have:

uri=imap://rag%40example.com@mail.example.com/From3e94fecf scope=imap://rag%40example.com@mail.example.com/INBOX terms=AND (from,ends with,mozilla.org) searchOnline=false uri=imap://rag%40example.com@mail.example.com/From%3A%20mozilla.org scope=imap://rag%40example.com@mail.example.com/INBOX terms=AND (from,ends with,mozilla.org) searchOnline=false

As far as I can tell, at least part of this is by design, because if I delete the "From: mozilla.org" saved search, and re-create it, the file ALWAYS has the the same name (e.g. "From3e94fecf.msf"). I had initially thought that this was a temp file that didn't get renamed, but, since it has the same name every time, I'm assuming the file name is being generated to prevent some conflict.

After a little experimentation, it appears that any folder name that appears similar to an rfc822 email header (i.e. a "name" followed by a colon, a space, and another "name")(e.g. "From: mozilla.org", "To: mozilla.org" and even "Foobar: mozilla.org") triggers this behavior.

As annoying as I find this behavior, I think it is highly unlikely anyone else could have experienced this without reporting it. I'm wondering if there's some advanced setting accessible from the config editor that somehow enabled some experimental feature that wasn't completely implemented. I have used this same profile for many years, through several upgrades of both the OS and thunderbird, and there may be a lot of cruft from previous versions in my profile.

Actually, as a further experiment I created a new temporary profile, and the behavior does NOT exist in the new profile (actually, the on disk file name is still munged, but, the user interface correctly shows the name of the virtual folder). So, apparently there IS some setting in my profile that is causing this behavior.

amanchesterman said

@ Zenos: the 'virtualFolders.dat' file exists in my profile whether or not I have a saved search folder in the folder pane, so I assume it's a standard part of a Linux installation.

It is a standard part of the "Unified" folder view as that is only a saved search. s new saved searches are appended to it.