Ok... I changed my config a little... to make it simpler.

I deleted the SYNOPTIC Namespace and all its Mailbox-Configurations and made the "Real" Namespace unhidden.

namespace Real {
prefix = Real/
separator = "/"
#hidden = yes
#list = no
# uncomment the following to debug, and comment the above
hidden = no
list = children
subscriptions = no
location = virtual:/var/mail/real:INDEX=/var/lib/dovecot/db/indexes/real/%u
ignore_on_failure = no
}

Thunderbird and doveadm shows me now all Mailboxes from the Real-Namespace:

# doveadm mailbox list -u jakob|grep Real
Real
Real/Archiv_zweijahr
Real/halbjahr
Real/Archiv
Real/einmonat
Real/zweimonat
Real/dreijahr
Real/zweijahr
Real/einjahr
Real/Alle

The dovecot-virtual from Real/Alle is

/var/mail/real: # cat Alle/dovecot-virtual
!INBOX
INBOX/*
-INBOX/Trash
-INBOX/Trash/*
-INBOX/Archives
-INBOX/Archives/*
-INBOX/Drafts
-INBOX/Drafts/*
-INBOX/Junk
-INBOX/Junk/*
-INBOX/SYSTEM
-INBOX/SYSTEM/*
all

When i try to open a Mailbox from them in Thunderbird i get this error in my logs (for example i opened Alle):

Jul 26 11:33:44 aldebaran dovecot[14873]: imap-login: Login: user=<jakob>, method=PLAIN, rip=92.60.9.18, lip=192.168.0.14, mpid=17347, TLS, session=<scQAseNxo3NcPAkS>
Jul 26 11:33:45 aldebaran dovecot[14873]: imap(jakob)<17347><scQAseNxo3NcPAkS>: Panic: file mail-index.c: line 752 (mail_index_close_nonopened): assertion failed: (index->views == NULL)
Jul 26 11:33:45 aldebaran dovecot[14873]: imap(jakob)<17347><scQAseNxo3NcPAkS>: Error: Raw backtrace: /usr/local/lib/dovecot/libdovecot.so.0(+0xcedf1) [0x7f1ba2b9bdf1] -> /usr/local/lib/dovecot/libdovecot.so.0(+
0xceeba) [0x7f1ba2b9beba] -> /usr/local/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7f1ba2b09fe8] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(+0xf7028) [0x7f1ba2d41028] -> /usr/local/lib/dovecot/libdovecot-s
torage.so.0(index_storage_mailbox_close+0x9a) [0x7f1ba2d1872a] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(mailbox_close+0x1a) [0x7f1ba2c961aa] -> /usr/local/lib/dovecot/lib20_virtual_plugin.so(+0xab80) [0
x7f1ba286db80] -> /usr/local/lib/dovecot/lib20_virtual_plugin.so(virtual_backend_box_open+0x2b) [0x7f1ba286dd3b] -> /usr/local/lib/dovecot/lib20_virtual_plugin.so(virtual_storage_sync_init+0x12a9) [0x7f1ba2870f1
9] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(mailbox_sync_init+0x51) [0x7f1ba2c986d1] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(mailbox_sync+0x37) [0x7f1ba2c98787] -> dovecot/imap [jakob 92.60.9.
18 select](cmd_select_full+0x17e) [0x55ab6bfb7ace] -> dovecot/imap [jakob 92.60.9.18 select](command_exec+0x64) [0x55ab6bfbf384] -> dovecot/imap [jakob 92.60.9.18 select](+0x1c832) [0x55ab6bfbd832] -> dovecot/im
ap [jakob 92.60.9.18 select](+0x1c8cc) [0x55ab6bfbd8cc] -> dovecot/imap [jakob 92.60.9.18 select](client_handle_input+0x1b5) [0x55ab6bfbdcd5] -> dovecot/imap [jakob 92.60.9.18 select](client_input+0xa4) [0x55ab6
bfbe2f4] -> /usr/local/lib/dovecot/libdovecot.so.0(io_loop_call_io+0x69) [0x7f1ba2bb4009] -> /usr/local/lib/dovecot/libdovecot.so.0(io_loop_handler_run_internal+0x12e) [0x7f1ba2bb58ce] -> /usr/local/lib/dovecot/
libdovecot.so.0(io_loop_handler_run+0x4c) [0x7f1ba2bb410c] -> /usr/local/lib/dovecot/libdovecot.so.0(io_loop_run+0x38) [0x7f1ba2bb4318] -> /usr/local/lib/dovecot/libdovecot.so.0(master_service_run+0x13) [0x7f1ba
2b2e413] -> dovecot/imap [jakob 92.60.9.18 select](main+0x331) [0x55ab6bfaff81] -> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7f1ba28efb17] -> dovecot/imap [jakob 92.60.9.18 select](_start+0x2a)
[0x55ab6bfb016a]
Jul 26 11:33:45 aldebaran dovecot[14873]: imap(jakob)<17347><scQAseNxo3NcPAkS>: Fatal: master: service(imap): child 17347 killed with signal 6 (core dumped)
Jul 26 11:33:45 aldebaran dovecot[14873]: imap-login: Login: user=<jakob>, method=PLAIN, rip=92.60.9.18, lip=192.168.0.14, mpid=17349, TLS, session=<RKUIseNxpHNcPAkS>
Jul 26 11:33:45 aldebaran dovecot[14873]: imap(jakob)<17349><RKUIseNxpHNcPAkS>: Panic: file mail-index.c: line 752 (mail_index_close_nonopened): assertion failed: (index->views == NULL)
Jul 26 11:33:45 aldebaran dovecot[14873]: imap(jakob)<17349><RKUIseNxpHNcPAkS>: Error: Raw backtrace: /usr/local/lib/dovecot/libdovecot.so.0(+0xcedf1) [0x7f5060afcdf1] -> /usr/local/lib/dovecot/libdovecot.so.0(+
0xceeba) [0x7f5060afceba] -> /usr/local/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7f5060a6afe8] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(+0xf7028) [0x7f5060ca2028] -> /usr/local/lib/dovecot/libdovecot-s
torage.so.0(index_storage_mailbox_close+0x9a) [0x7f5060c7972a] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(mailbox_close+0x1a) [0x7f5060bf71aa] -> /usr/local/lib/dovecot/lib20_virtual_plugin.so(+0xab80) [0
x7f50607ceb80] -> /usr/local/lib/dovecot/lib20_virtual_plugin.so(virtual_backend_box_open+0x2b) [0x7f50607ced3b] -> /usr/local/lib/dovecot/lib20_virtual_plugin.so(virtual_storage_sync_init+0x12a9) [0x7f50607d1f1
9] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(mailbox_sync_init+0x51) [0x7f5060bf96d1] -> /usr/local/lib/dovecot/libdovecot-storage.so.0(mailbox_sync+0x37) [0x7f5060bf9787] -> dovecot/imap [jakob 92.60.9.
18 select](cmd_select_full+0x17e) [0x557131605ace] -> dovecot/imap [jakob 92.60.9.18 select](command_exec+0x64) [0x55713160d384] -> dovecot/imap [jakob 92.60.9.18 select](+0x1c832) [0x55713160b832] -> dovecot/im
ap [jakob 92.60.9.18 select](+0x1c8cc) [0x55713160b8cc] -> dovecot/imap [jakob 92.60.9.18 select](client_handle_input+0x1b5) [0x55713160bcd5] -> dovecot/imap [jakob 92.60.9.18 select](client_input+0xa4) [0x55713
160c2f4] -> /usr/local/lib/dovecot/libdovecot.so.0(io_loop_call_io+0x69) [0x7f5060b15009] -> /usr/local/lib/dovecot/libdovecot.so.0(io_loop_handler_run_internal+0x12e) [0x7f5060b168ce] -> /usr/local/lib/dovecot/
libdovecot.so.0(io_loop_handler_run+0x4c) [0x7f5060b1510c] -> /usr/local/lib/dovecot/libdovecot.so.0(io_loop_run+0x38) [0x7f5060b15318] -> /usr/local/lib/dovecot/libdovecot.so.0(master_service_run+0x13) [0x7f506
0a8f413] -> dovecot/imap [jakob 92.60.9.18 select](main+0x331) [0x5571315fdf81] -> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7f5060850b17] -> dovecot/imap [jakob 92.60.9.18 select](_start+0x2a)
[0x5571315fe16a]
Jul 26 11:33:45 aldebaran dovecot[14873]: imap(jakob)<17349><RKUIseNxpHNcPAkS>: Fatal: master: service(imap): child 17349 killed with signal 6 (core dumped)

Jakob

Gesendet: Donnerstag, 26. Juli 2018 um 11:26 Uhr
Von: "Aki Tuomi" <aki.tuomi@dovecot.fi>
An: wertstoffe@nurfuerspam.de, dovecot@dovecot.org
Betreff: Re: Aw: Re: Panic: Leaked view for index - virtual mailbox

I am pretty sure Synoptic/INBOX/Archives will not be same as INBOX/Archives.

a SELECT Synoptic/INBOX/Archives
a NO Mailbox doesn't exist: Synoptic/INBOX/Archives (0.001 + 0.000 secs).

a SELECT INBOX/Archives
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permitted.
* 45 EXISTS

So as you can see, specifying 'INBOX/Archives' under 'Synoptic' namespace means it will not be the same as INBOX/Archives. It is a separate mailbox, and the only way it can work is if you have INBOX/Archives/dovecot-virtual file which specifies that it reads & writes to INBOX/Archives. This is not the way to make some kind of fancy aliasing.

I took a stab at reproducing your issue, but so far no luck. I have to try including the Archiv namespace as well.

Aki

On 26.07.2018 12:01, wertstoffe@nurfuerspam.de wrote:

Hello!

(and sorry for double mailings... i have some troubles with my mailprovider 1&1... :-/ )
Yes, i have for all of them similar Folders and Configurations. But i thought, it was to much to send you, because, they all are similar.

There is one Namespace "Real" with according Folder in /var/mail/real.
This Namespace is hidden to the User. It is used to "prepare" the views to the emails. All Emails, only all emails from the last month, halfyear, year, 2 years and so on. The Archive in the dovecot-virtual config in "Archiv" is a separate Namespace. (look below)

/var/mail/real: # l
insgesamt 0
drwxr-sr-x 1 vmail vmail 30 Jul 12 17:47 Alle
drwxr-sr-x 1 vmail vmail 30 Jul 10 00:06 Archiv
drwxr-sr-x 1 vmail vmail 30 Jul 10 00:06 Archiv_zweijahr
-rw-r--r-- 1 vmail vmail 0 Nov 27 2017 dovecot-acl-list
drwxr-sr-x 1 vmail vmail 30 Jul 12 11:06 dreijahr
drwxr-sr-x 1 vmail vmail 30 Jul 12 11:06 einjahr
drwxr-sr-x 1 vmail vmail 30 Jul 10 00:06 einmonat
drwxr-sr-x 1 vmail vmail 30 Jul 12 17:46 halbjahr
drwxr-sr-x 1 vmail vmail 30 Jul 12 11:06 zweijahr
drwxr-sr-x 1 vmail vmail 30 Jul 10 00:06 zweimonat

For example:
/var/mail/real: # cat Alle/dovecot-virtual
!INBOX
INBOX/*
-INBOX/Trash
-INBOX/Trash/*
-INBOX/Archives
-INBOX/Archives/*
-INBOX/Drafts
-INBOX/Drafts/*
-INBOX/Junk
-INBOX/Junk/*
-INBOX/SYSTEM
-INBOX/SYSTEM/*
all

The "All-Mailbox" for only one year:
/var/mail/real: # cat einjahr/dovecot-virtual
!Real/Alle
all younger 31536000

The others "zweijahr", "halbjahr" and so on keep the same definition, but with other count of seconds... this is for playing around, which is the best period to hold in the "AKTUELLE" Mailbox in Synoptic. And to choose in Thunderbird or other Mailclients, for faster syncing or more emails.

and the Archiv:
/var/mail/real: # cat Archiv/dovecot-virtual
Archiv/*
all

And now the other Folder /var/mail/virtual, which contains the Namespace "SYNOPTIC". Here i collect different Views for my emails. This Namespace is shown to the User, and i can subscribe them in the MUA.

/var/mail/virtual: # cat AKTUELL/dovecot-virtual
!Real/halbjahr
all

/var/mail/virtual: # cat ARCHIV/dovecot-virtual
Archiv
Archiv/*
all younger 1261440000

/var/mail/virtual: # cat Ungelesene/dovecot-virtual
Real/Alle
unseen

/var/mail/virtual: # cat Sent/dovecot-virtual
!INBOX/Sent
INBOX/Sent/*
all

and the Namespace "Archive" is located in
/var/mail/archiv
and contains all archieved emails. (There are really a lot Emails).
I declare this Namespace as "Special Folder", so Thunderbird picks it up as the Archive-Folder for automatic archieving old emails.

The thing is, I get the error on the "Alle", "Send", "ungelesene"... Mailboxes. The Archiv-Mailbox is working correctly!

Another funny thing is... I got this error on older versions and also on version 2.4 (=master in git). But not all the time.
Some day it worked without error... It worked until i deleted the whole index-directories a few days ago... then i got the error. Without changing the config!!

Uhmm... Yes, there is this Synoptic/INBOX/Archives Mailbox. This is for a special Mailclient "K9Mail" (on Android). Because i used there only the Synoptic-Namespace. And K9Mail created itself an own Archive-Folder, if there is no one below INBOX. With this solution, K9Mail shows the same Archive as Thunderbird shows ist as Special folder.

The Gmail-App handles different Namespaces at the same time, but cannot handle different Identities.
K9Mail can handle different Identities (for Alias-Emailadresses) for the same Account, but only one Namespace...

Jakob