- dovecot - dovecot.org

Proxying of non "plain" SASL mechnisms.
by Peter Mogensen 18 Mar '15

18 Mar '15

Hi, I understand from earlier discussions that the reason dovecot doesn't support proxying of other SASL mechanisms than those which supply the plaintext password is that in general it would be possible to proxy any SASL mechanism since it might protect against man-in-the-middle attacks (which would prevent proxying). However, that has led to choice between letting users use PLAIN (or equivalent), or to have the proxy access the target hosts by "master" password. Of course, having the plaintext password the proxy could in principle do other challenge/response SASL handshakes with the target backend, but right now only LOGIN and PLAIN is implemented. So I wondered about the rationale for not just forward the SASL handshake. - First, blindly forwardning will not do, since the mech data has to be decoded anyway to do any per/user passdb lookup (to, say, find the target host). But you don't need authentication to actually succeed to do that. You only need AuthZ-id or AuthN-id. - Secondly, the design of the interaction between imap-login processes and the auth-service in general prevent in general to forward multi-handshake SASL mechanisms, since the authentication must be done before the proxying can be started. But it doesn't prevent forwarding of single handshake SASL mechanisms which use SASL-IR. - Thirdly, while it's correct that some SASL mechanisms protect against man-in-the-middle attacks, that doesn't apply for most single-handshake SASL-IR mechanisms unless they do some kind of channel-binding. (like SASL EXTERNAL) For example, the GS2-KRB5 SASL mech would be perfectly forwarded if just the Kerberos ticket doesn't put restrictions on the client IP-address. So, why not just extend the support for proxy authentication forwarding to any single-handskake SASL-IR mechanism, which doesn't use channel-binding? (which includes PLAIN, but also GS2-KRB5, and possibly others). /Peter

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Dovecot 2.2.15 issues with global ACL
by Ovidiu Moldovan 18 Mar '15

18 Mar '15

Hello, We have upgraded from Dovecot 2.2.13 to 2.2.15 and we are using global ACL file. The content of the ACL file is as following: * owner r INBOX owner lrwstipekxa INBOX/* owner lrwstipekxa user owner rwstipekxa user/* owner rwstipekxa This worked fine but after update any user cannot see any folders from under the INBOX, also they cannot create any new folders. Error into the logs are like this: Debug: acl: Mailbox not in dovecot-acl-list: INBOX Debug: acl: Mailbox not in dovecot-acl-list: INBOX/Chats Debug: acl: Mailbox not in dovecot-acl-list: INBOX/Draft Debug: acl: Mailbox not in dovecot-acl-list: INBOX/INBOX .... I can only see one acl change log at version 2.2.14: http://www.dovecot.org/list/dovecot-news/2014-October/000276.html acl: Global ACL file now supports "quotes" around patterns. But I could not find the reason why the global acl file does not work anymore? Br, Ova

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http://xi.rename-it.nl 2.2.16-1~auto+10/11/12/13: segfault /var/lib/dovecot/auth OR (db_ldap_connect_delayed):
by Denny Fuchs 17 Mar '15

17 Mar '15

hi, I testing around with Kolab with LDAP and have some strange problems, with the auto generated packages for Wheezy. On my first test VM, I have 2:2.2.16~rc1-1~auto+4 installed, and everything works as expected. On a new VM I have 2.2.16-1~auto+13_amd64.deb packages and if I include LDAP backend, I get a segmentation fault on /usr/lib/dovecot/auth: root@kolab:/etc/dovecot/conf.d# /usr/lib/dovecot/auth Segmentation fault with auto+12 and auto+13 If I downgrade to auto+11 or auto+10 I get: Mar 17 14:42:59 kolab dovecot: auth: Panic: file db-ldap.c: line 1228 (db_ldap_connect_delayed): assertion failed: (conn->to == NULL) Mar 17 14:42:59 kolab dovecot: auth: Error: Raw backtrace: /usr/lib/dovecot/libdovecot.so.0(+0x7b5ef) [0x7f57d815c5ef] -> /usr/lib/dovecot/libdovecot.so.0(+0x7b64e) [0x7f57d815c64e] -> /usr/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7f57d810b0d5] -> /usr/lib/dovecot/modules/auth/libauthdb_ldap.so(+0x5455) [0x7f57d70e2455] -> dovecot/auth(userdb_init+0x1a) [0x42765a] -> dovecot/auth(auths_init+0xc9) [0x40d979] -> dovecot/auth(main+0x2b5) [0x40cc85] -> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xfd) [0x7f57d7523ead] -> dovecot/auth() [0x40cee9] Mar 17 14:42:59 kolab dovecot: auth: Fatal: master: service(auth): child 1161 killed with signal 6 (core dumps disabled) Mar 17 14:42:59 kolab dovecot: master: Error: service(auth): command startup failed, throttling for 2 secs Mar 17 14:42:59 kolab dovecot: pop3-login: Disconnected: Auth process broken (disconnected before auth was ready, waited 0 secs): user=<>, rip=::1, lip=::1, secured, session=<1QMUJXwRTQAAAAAAAAAAAAAAAAAAAAAB> ii dovecot-sieve 2:2.2.16~rc1-1~auto+4 amd64 secure POP3/IMAP server - Sieve filters support root@kolab:/# ldd /usr/lib/dovecot/modules/auth/libauthdb_ldap.so linux-vdso.so.1 => (0x00007ffc4a1c6000) libldap_r-2.4.so.2 => /usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2 (0x00007effe2d1a000) librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007effe2b12000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007effe2786000) liblber-2.4.so.2 => /usr/lib/x86_64-linux-gnu/liblber-2.4.so.2 (0x00007effe2577000) libresolv.so.2 => /lib/x86_64-linux-gnu/libresolv.so.2 (0x00007effe2361000) libsasl2.so.2 => /usr/lib/x86_64-linux-gnu/libsasl2.so.2 (0x00007effe2145000) libgnutls.so.26 => /usr/lib/x86_64-linux-gnu/libgnutls.so.26 (0x00007effe1e85000) libgcrypt.so.11 => /lib/x86_64-linux-gnu/libgcrypt.so.11 (0x00007effe1c06000) libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007effe19e9000) /lib64/ld-linux-x86-64.so.2 (0x00007effe3180000) libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007effe17e5000) libtasn1.so.3 => /usr/lib/x86_64-linux-gnu/libtasn1.so.3 (0x00007effe15d3000) libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007effe13bc000) libp11-kit.so.0 => /usr/lib/x86_64-linux-gnu/libp11-kit.so.0 (0x00007effe11aa000) libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007effe0fa6000) Then I copied from my first VM the libauthdb_ldap.so file on the new test VM to /usr/lib/dovecot/modules/auth/libauthdb_ldap.so (remember: ~rc1-1~auto+4) and the result: root@kolab:/etc/dovecot/conf.d# /usr/lib/dovecot/auth Error: LDAP: binding failed (dn cn=Directory Manager): Invalid credentials and, it works again ... linux-vdso.so.1 => (0x00007fffa00c6000) libldap_r-2.4.so.2 => /usr/lib/x86_64-linux-gnu/libldap_r-2.4.so.2 (0x00007f94b7ec3000) librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f94b7cbb000) libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f94b792f000) liblber-2.4.so.2 => /usr/lib/x86_64-linux-gnu/liblber-2.4.so.2 (0x00007f94b7720000) libresolv.so.2 => /lib/x86_64-linux-gnu/libresolv.so.2 (0x00007f94b750a000) libsasl2.so.2 => /usr/lib/x86_64-linux-gnu/libsasl2.so.2 (0x00007f94b72ee000) libgnutls.so.26 => /usr/lib/x86_64-linux-gnu/libgnutls.so.26 (0x00007f94b702e000) libgcrypt.so.11 => /lib/x86_64-linux-gnu/libgcrypt.so.11 (0x00007f94b6daf000) libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f94b6b92000) /lib64/ld-linux-x86-64.so.2 (0x00007f94b8328000) libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f94b698e000) libtasn1.so.3 => /usr/lib/x86_64-linux-gnu/libtasn1.so.3 (0x00007f94b677c000) libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f94b6565000) libp11-kit.so.0 => /usr/lib/x86_64-linux-gnu/libp11-kit.so.0 (0x00007f94b6353000) libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007f94b614f000) So, it seems, that there is something broken with the autogenerated packages, or with my fresh installed Wheey VM (KVM AMD64) in combination with LDAP. any suggestions? cu denny

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Dovecot current number of connections being used.
by Jaime Ventura 17 Mar '15

17 Mar '15

Hey, Is there an easy way to get how many connections are being handled at a moment? I wanted to have that number over the time and see: - Trends on usage during the day - how close is it from reaching the maximum number of connections. - ... I'm searching for a solution without recurring to something like netstat | grep imap | wc -l. Thanks, Jaime

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Patch SERVICE_FIRST_STATUS_TIMEOUT
by Andre Helwig 17 Mar '15

17 Mar '15

Hi list, we had a lot of trouble with our Dovecot Replicating-Cluster installation authenticating against LDAP Service. We ran in a timeout and what happened was that we got more and more search requests running against on our ldap server. And on the dovecot site the process got killed after a couple of seconds. So we ran into a race condition and our LDAP Server was under heavy load. We got a log entry like this: "Initial status notification not received in 30 seconds, killing the process" So we had to apply the attached patch to our Source based Dovecot Cluster. Could you please make a configurable Parameter for our Patched value? That would be great to get this parameter Configurable. Thanks Andre Helwig -- Heinlein Support GmbH Schwedter Str. 8/9b, 10119 Berlin http://www.heinlein-support.de Tel: 030 / 405051-0 Fax: 030 / 405051-19 Zwangsangaben lt. §35a GmbHG: HRB 93818 B / Amtsgericht Berlin-Charlottenburg, Geschäftsführer: Peer Heinlein -- Sitz: Berlin

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Dovecot 2.1.7 still accepting SSLv3 though disabled?
by Thomas Preissler 17 Mar '15

17 Mar '15

Hello, I came across a strange problem with my Dovecot 2.1.7 installation (updated Debian Wheezy) in regards to SSL/TLS connections. My configuration is as follows: $ dovecot -n | grep ssl service imap-login { ssl = yes ... } ssl_cert = <...... ssl_cipher_list = EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA ssl_key = <...... ssl_protocols = !SSLv3 !SSLv2 This cipherstring has been taken from https://bettercrypto.org/static/applied-crypto-hardening.pdf. But this is not the problem, when I comment it out, Dovecot still behaves the same way. When I enable verbose_ssl I get this: 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x10, ret=1: before/accept initialization [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: before/accept initialization [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2002, ret=-1: unknown state [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 read client hello A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 write server hello A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 write certificate A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 write server done A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 flush data [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2002, ret=-1: SSLv3 read client certificate A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2002, ret=-1: SSLv3 read client certificate A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 read client key exchange A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 read finished A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 write change cipher spec A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 write finished A [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2001, ret=1: SSLv3 flush data [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x20, ret=1: SSL negotiation finished successfully [$CLIENTIP] 2015-03-15 08:27:39 imap-login: Warning: SSL: where=0x2002, ret=1: SSL negotiation finished successfully [$CLIENTIP] Is this right? Is SSLv3 used on this connection? But when I explicitely test for SSLv3 support I get $ openssl s_client -connect $SERVERIP:993 -ssl3 CONNECTED(00000003) 140683835029160:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1260:SSL alert number 40 140683835029160:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:598: --- no peer certificate available --- No client certificate CA names sent --- SSL handshake has read 7 bytes and written 0 bytes --- New, (NONE), Cipher is (NONE) Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE SSL-Session: Protocol : SSLv3 Cipher : 0000 Session-ID: Session-ID-ctx: Master-Key: Key-Arg : None PSK identity: None PSK identity hint: None SRP username: None Start Time: 1426411304 Timeout : 7200 (sec) Verify return code: 0 (ok) --- Where I got this from says "if you you get a handshake failure, then you don't support SSLv3". But in my case the following output kinda says, that I do support it - with a ciphers of (NONE)? In regards to libraries $ ldd /usr/lib/dovecot/imap-login | grep ssl libssl.so.1.0.0 => /usr/lib/x86_64-linux-gnu/libssl.so.1.0.0 (0x00007f1f55025000) $ dpkg -l | grep ssl ii libcrypt-openssl-bignum-perl 0.04-3 amd64 Access OpenSSL multiprecision integer arithmetic libraries ii libcrypt-openssl-dsa-perl 0.13-6 amd64 module which implements the DSA signature verification system ii libcrypt-openssl-rsa-perl 0.28-1 amd64 module for RSA encryption using OpenSSL ii libcrypt-ssleay-perl 0.58-1 amd64 OpenSSL support for LWP ii libio-socket-ssl-perl 1.76-2 all Perl module implementing object oriented interface to SSL sockets ii libnet-ssleay-perl 1.48-1+b1 amd64 Perl module for Secure Sockets Layer (SSL) rc libssl0.9.8 0.9.8o-4squeeze14 amd64 SSL shared libraries ii libssl1.0.0:amd64 1.0.1e-2+deb7u14 amd64 SSL shared libraries ii openssl 1.0.1e-2+deb7u14 amd64 Secure Socket Layer (SSL) binary and related cryptographic tools ii openssl-blacklist 0.5-3 all Blacklists for OpenSSL RSA keys and tools ii python-openssl 0.13-2+deb7u1 amd64 Python 2 wrapper around the OpenSSL library ii ssl-cert 1.0.32 all simple debconf wrapper for OpenSSL ii ssl-cert-check 3.22-1 all proactively handling X.509 certificate expiration ii sslmate 0.6.2-1 all Buy and manage SSL certificates from the command line My NginX is using the same library, and this does indeed support TLSv2, so what I am doing wrong in my Dovecot configuration? Any clues? Regards Thomas -- www.preissler.co.uk | Twitter: @module0x90 | PGP-Key: 75889415 GPG Fingerprint: CCBD 153A D257 CA7E A217 FDF7 5928 03D1 7588 9415

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Released Pigeonhole v0.4.7.rc3 for Dovecot v2.2.16
by Stephan Bosch 17 Mar '15

17 Mar '15

Hello Dovecot users, The rc2 release had a couple of new, rather small, but very annoying bugs. First of all, the path for a file storage wasn't actually normalized, due to a stupid last-minute change before the release. This caused the personal script to be skipped with a warning when there were e.g. duplicate slashes in the path. Second, due to recent changes, the file storage would complain with a temporary error if the directory where the active script symlink would be located was missing. Changelog v0.4.7 (unchanged): * editheader extension: Made protection against addition and deletion of headers configurable separately. Also, the `Received' and `Auto-Submitted' headers are no longer protected against addition by default. * Turned message envelope address parse errors into warnings. * The interpreter now accepts non-standard domain names, e.g. containing '_'. + Implemented the Sieve index extension (RFC 5260). + Implemented support for the mboxmetadata and servermetadata extensions (RFC 5490). + Implemented new sieve commands for the doveadm command line utility. These commands are currently limited to ManageSieve operations, but the other current sieve tools will be migrated to doveadm in the near future as well. + Added more debug output about binary up-to-date checking. + Added script metadata to binary dump output. - Fixed Sieve script binary up-to-date checking by normalizing the script location. - The Sieve interpreter now flushes the duplicate database during start phase of result execution rather than commit phase. This makes sure locks on the duplicate database are released as soon as possible, preventing contention. - Performed a few optimizations in the lexical scanner of the language. - Fixed bug in `:matches' match-type that made a pattern without wildcards match as if there were a '*' at the beginning. - Fixed crash in validation of the string parameter of the comparator tag. - extprograms extension: Made sure supplemental group privileges are also dropped. This was a problem reported by Debian lintian. - Fixed bug in handling of binary errors for action side-effects and message overrides. - file script storage: Restructured storage initialization to address backwards compatibility issues. - dict script storage: Fixed small memory allocation bug. The release is available as follows: http://pigeonhole.dovecot.org/releases/2.2/dovecot-2.2-pigeonhole-0.4.7.rc3… http://pigeonhole.dovecot.org/releases/2.2/dovecot-2.2-pigeonhole-0.4.7.rc3… Refer to http://pigeonhole.dovecot.org and the Dovecot v2.x wiki for more information. Have fun testing this new release and don't hesitate to notify me when there are any problems. Regards, -- Stephan Bosch stephan(a)rename-it.nl

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Released Pigeonhole v0.4.7.rc2 for Dovecot v2.2.16
by Stephan Bosch 16 Mar '15

16 Mar '15

Hello Dovecot users, The rc1 release showed a few problems with the up-to-date checking of on-disk binary files. The binary files contain some metadata about the script these were compiled from. If this doesn't match the current script anymore, the script is recompiled. One of these metadata items is the script location. However, this location wasn't normalized, so when the binary would be compiled with sievec it depended on the path provided at the command line. When dumping a script binary, the metadata is now printed as well. Also, I added more debug log lines about up-to-date checking. I improved backwards compatibility for the file script storage a bit relative to the last version. It now properly recognizes a regular file at the symlink path, even when the storage path itself doesn't exist. Changelog v0.4.7 (updated): * editheader extension: Made protection against addition and deletion of headers configurable separately. Also, the `Received' and `Auto-Submitted' headers are no longer protected against addition by default. * Turned message envelope address parse errors into warnings. * The interpreter now accepts non-standard domain names, e.g. containing '_'. + Implemented the Sieve index extension (RFC 5260). + Implemented support for the mboxmetadata and servermetadata extensions (RFC 5490). + Implemented new sieve commands for the doveadm command line utility. These commands are currently limited to ManageSieve operations, but the other current sieve tools will be migrated to doveadm in the near future as well. + Added more debug output about binary up-to-date checking. + Added script metadata to binary dump output. - Fixed Sieve script binary up-to-date checking by normalizing the script location. - The Sieve interpreter now flushes the duplicate database during start phase of result execution rather than commit phase. This makes sure locks on the duplicate database are released as soon as possible, preventing contention. - Performed a few optimizations in the lexical scanner of the language. - Fixed bug in `:matches' match-type that made a pattern without wildcards match as if there were a '*' at the beginning. - Fixed crash in validation of the string parameter of the comparator tag. - extprograms extension: Made sure supplemental group privileges are also dropped. This was a problem reported by Debian lintian. - Fixed bug in handling of binary errors for action side-effects and message overrides. - file script storage: Restructured storage initialization to address backwards compatibility issues. - dict script storage: Fixed small memory allocation bug. The release is available as follows: http://pigeonhole.dovecot.org/releases/2.2/dovecot-2.2-pigeonhole-0.4.7.rc2… http://pigeonhole.dovecot.org/releases/2.2/dovecot-2.2-pigeonhole-0.4.7.rc2… Refer to http://pigeonhole.dovecot.org and the Dovecot v2.x wiki for more information. Have fun testing this new release and don't hesitate to notify me when there are any problems. Regards, -- Stephan Bosch stephan(a)rename-it.nl

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Warning: sieve: file storage: Active sieve script symlink is broken: Invalid/unknown path to storage
by Василий Севостьянов 16 Mar '15

16 Mar '15

dovecot version: 2.2.16 (3d8a054a93a9) sieve configuration: plugin { sieve = ~/.dovecot.sieve sieve_dir = ~/sieve } For each of the users, ~/.dovecot.sieve is a symlink to ~/sieve/roundcube.sieve Until yesterday, everything was working find. But starting from yesterday's update, the log is filling up with messages like: Mar 16 19:12:32 cs12986 dovecot: lda(postmaster(a)contoso.com <postmaster(a)euro-contact.ru>): Warning: sieve: file storage: Active sieve script symlink /home/virtualmail/contoso.com/it/.dovecot.sieve <http://euct.ru/it/.dovecot.sieve> is broken: Invalid/unknown path to storage (points to /home/virtualmail/contoso.com/it/sieve <http://euct.ru/it/sieve>). Nothing was changed in the config files. What might have gone wrong?

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Configuring Shared Mailbox Dictionaries
by james＠lottspot.com 16 Mar '15

16 Mar '15

Hello, list! I am in the midst of configuring a new Dovecot IMAP server, and I'm preparing to setup shard mailboxes as part of the ocnfiguration. In order to get these setup the way I want, I've figured out that I'm going to have to setup an acl_shared_dict. This is where things start to get confusing for me, as I have had difficulty finding thorough explanations of dictionary configuration. My primary concern is that all my user details are stored in a sqlite database in which the '%n' and '%d' components of username/email addresses are stored in separate columns. The SQL dictionary example in the Shared Mailboxes document [http://wiki2.dovecot.org/SharedMailboxes/Shared] assumes that the username is stored as a singular '%n@%d' key. In my authdb lookups, I use sqlite syntax to concatenate the '%n' and '%d' columns around a '@' character to find the user. Is it possible to implement an acl_shared_dict in some similar fashion? My second question, which is completely unrelated and more out of morbid curiosity than anything (although it could affect my configuration decisions) is that I noticed every dictionary which shows up in the documentation has a "pattern" field. In the case of the acl_shared_dict example, the pattern is 'shared/shared-boxes/user/$to/$from'. I couldn't figure out by studying the example where this value was derived from, or indeed where it is derived from in any example dictionaries which are documented. Can anyone explain the meaning of the "pattern" field and what exactly its value means? Thanks in advance for all your helpful answers! :)

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