Hi Sami, On Sun, 9 Sep 2018, Sami Ketola wrote:> Is it possible to get imapc rawlogs to analyze? create a directory that > is writeable and add -o imapc_rawlog_dir=/path/to/directory to command > line.Tried that. Thanks for the suggestion, that is actually really helpful. If anyone wants to play along at home, the files in that directory are created with the permissions of mail_uid/mail_gid. The dir should be world-writable to make it easy.> Also with recent dovecot release you can tell dsync which header fields > to hash when matching mails. Add dsync_hashed_headers=Message-ID to > config and dovecot will only mach mails using Message-ID header fileld.I had seen that parameter but thought it would be prudent to not _just_ rely on the Message-ID but instead keep the default "Date Message-ID". I _think_ I might have found an issue when looking at the log: 1536525811.026071 * 39 FETCH (UID 39 BODY[HEADER.FIELDS (Date Message-ID)] {159} 1536525811.026071 Message-ID: <Pine.LNX.4.30.0207091925420.433-100000 at trinity.knopfdruck.org> 1536525811.026071 Date: Tue, 9 Jul 2002 19:26:04 +0200 (MEST) 1536525811.026071 Date: Tue, 9 Jul 2002 12:36:13 +0200 1536525811.026071 1536525811.026071 ) A duplicate Date header is certainly unexpected. Having a look at the original mail on disk on the Cyrus server shows the following Mail:>From [redacted] Tue Jul 9 19:26:04 2002X-Sieve: cmu-sieve 1.3 Return-Path: [redacted] Received: from bender.bawue.de (localhost [127.0.0.1]) by bender.bawue.de (Postfix) with ESMTP id C79CE48CBC; Tue, 9 Jul 2002 19:29:08 +0200 (CEST) Delivered-To: [redacted] Received: from [redacted] by bender.bawue.de (Postfix) with ESMTP id CFA4848CAA for [redacted]; Tue, 9 Jul 2002 19:28:43 +0200 (CEST) From: [redacted] X-Sender: [redacted] To: [redacted] Message-ID: <Pine.LNX.4.30.0207091925420.433-100000 at trinity.knopfdruck.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Subject: [redacted] Date: Tue, 9 Jul 2002 19:26:04 +0200 (MEST) Status: RO X-Status: X-Keywords: X-UID: 38 ---------- Forwarded message ---------- Date: Tue, 9 Jul 2002 12:36:13 +0200 Subject: Gewinn [redacted] So it looks like the Cyrus imapd is incorrectly parsing the mail and returning the body content as a header. Comparing the content of UID 39 on the remote server will then hash differently than the UID 39 on the local dovecot server, which behaves better and only returns a single date header. Following the robustness principle it feels to me that it would make sense for dsync to disregard a duplicate header from a remote server and only use the first occurence. Would that be a good approach to the problem? Now that I understand the problem I am having, I can just workaround it but it seems to me that dsync should handle this case better. Anyway, thanks a lot for the imapc_rawlog_dir hint, that helped a lot. cheers, Andreas
> On 10 Sep 2018, at 0.05, Andreas Thienemann <andreas at thienemann.net> wrote: > > Following the robustness principle it feels to me that it would make sense for dsync to disregard a duplicate header from a remote server and only use the first occurence. > > Would that be a good approach to the problem? Now that I understand the problem I am having, I can just workaround it but it seems to me that dsync should handle this case better. >Currently dovecot does rely on remote to send valid RFC-compliant headers. But you are not alone, we have seen similar problems with mixed header fields on some legacy servers on the migrations we have performed. I have found dsync_hashed_headers setting as a good workaround for migrating mails from broken imap servers. As per RFC Message-ID should be unique and we have safely used setting dsync_hashed_headers=Message-ID to migrate the problematic users away from the broken servers. Sami
Hi Sami, On Mon, 10 Sep 2018, Sami Ketola wrote:> Currently dovecot does rely on remote to send valid RFC-compliant > headers. But you are not alone, we have seen similar problems with mixed > header fields on some legacy servers on the migrations we have > performed.Bummer. Would have been _very_ cool if doveadm could just disregard a second copy of a header sent.> I have found dsync_hashed_headers setting as a good workaround for > migrating mails from broken imap servers. As per RFC Message-ID should > be unique and we have safely used setting > dsync_hashed_headers=Message-ID to migrate the problematic users away > from the broken servers.There's a certain irony in hoping that Message-ID headers are RFC compliant while we're talking to a non-RFC compliant mailserver. ;-) That being said, limiting dsync_hashed_headers to only look at the Message-ID _does_ seem to do the trick. But just to clarify: As far as I read the sourecode, the logic is as follows: Fetch UID on remote, hash headers. Fetch UID on local, hash headers. Compare that header hashes match _for this one UID_. If yes, good. If not, something has changed. This means there's no comparing the hashed headers to other UIDs going on? e.g. someone having two copies of the same mail with the same Message-ID would _not_ lead to an error, as these are saved under different UIDs. Is my understanding of the code correct? cheers, Andreas
Hi Sami, On Mon, 10 Sep 2018, Sami Ketola wrote:> I have found dsync_hashed_headers setting as a good workaround for > migrating mails from broken imap servers. As per RFC Message-ID should > be unique and we have safely used setting > dsync_hashed_headers=Message-ID to migrate the problematic users away > from the broken servers.Just for the record, limiting the dsync_hashed_headers to _just_ the Message-ID is not a good solution. Turns out, I also get the situation where Cyrus will happily sent multiple Message-IDs: * 797 FETCH (UID 797 BODY[HEADER.FIELDS (Message-ID)] {127} Message-Id: <200404140548.i3E5mYb11123 at c2.hrz.uni-giessen.de> Message-Id: <CFA82361-8CB4-11D8-A4CA-000393101422 at MeinBu.ch> ) 1 OK Completed (0.000 sec) My workaround now is to just ensure that I run an uneven number of doveadm backup runs, triggering a full sync of problematic folders. The uneven runs delete the folders, the even ones transfer... Anyway, thanks for the suggestion, it was a good attempt. ;-) cheers, Andreas