Re: Dovecot Oy merger with Open-Xchange AG

[Nick Edwards]

On 3/24/15, Adrian Zaugg  wrote:
> I think everyone shares your concerns. But there are no rules that the
> outcome of this merger must get something bad, so let's see what
> happens. I hope that it's true what Timo said and that dovecot can
> evolve and get even better as it is today. Good luck guys!
>

Indeed, and quite the opposite to MySQL when we all knew that oracle
would destroy it or constrain it, before Sun sold out to them, and
what we all forecast of course came true, oracle has done so badly
with it, its original author Monty came back with a fork, one that
every distro just about has changed to! Infact I dont know anyone
using mysql today, most sane admins moved to mariadb where it is in
safe hands. hopefuly Timo has a legal  back door open to do the same
should things change and go hte way mysql did.

Re: quota setup assistance (postfix+dovecot+mysql)

[Gedalya]

On 03/24/2015 12:50 AM, rooster wrote:

10-mail.conf : mail_plugins = $mail_plugins zlib quota

15-lda.conf : mail_plugins = $mail_plugins sieve

20-imap.conf : mail_plugins = $mail_plugins imap_zlib imap_quota antispam

20-lmtp.conf : mail_plugins = $mail_plugins sieve


If the above are the correct settings, why do I get the following 
errors?

Mar 23 00:55:31 host dovecot: lmtp(328): Debug: Module loaded: 
/usr/lib/dovecot/modules/lib10_quota_plugin.so
Mar 23 00:55:31 host dovecot: lmtp(328): Error: 
dlopen(/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so) failed: 
/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so: undefined symbol: 
command_unregister
Mar 23 00:55:31 host dovecot: lmtp(328): Fatal: Couldn't load required plugins


Doesn't make much sense. If that's the current config (and you restarted 
dovecot) then that shouldn't be happening. A good way to understand 
dovecot's config as it actually got applied is to run 'doveconf -n', try 
to review the output, and post here after masking out private info if 
you need further help.

Re: quota setup assistance (postfix+dovecot+mysql)

[rooster]

> On 2015-03-23, at 3:38 PM, Gedalya  wrote:
> 
> That idea is to set the global mail_plugins to contain the plugins you would 
> want enabled in *all* places. If there is not a single such plugin, then 
> indeed you can set the global mail_plugins to empty, but then you should 
> still use $mail_plugins everywhere because then it would just work, should 
> you ever add a plugin to the global list.

That makes sense. :)



>>  protocol lda {
>>  mail_plugins =
> I don't see why you shouldn't add quota here, and zlib too in your case. If 
> you don't use lda at all, it still won't hurt.

I’m certain it is set. I will confirm my current configuration in each 
file and post the results.

> Finally, doveadm is sort of a "protocol" too and any protocol for which you 
> did not specify its own "mail_plugins = ..." will use the global value itself.
> So for example here you explicitly turned off all plugins for lda, overriding 
> the global value. And doveadm will use the global value. So just take it all 
> into consideration.

Thank you for the tidbit. That is good to know.


Here are the currently set parameters for mail_plugins in each config file :

10-mail.conf : mail_plugins = $mail_plugins zlib quota

15-lda.conf : mail_plugins = $mail_plugins sieve

20-imap.conf : mail_plugins = $mail_plugins imap_zlib imap_quota antispam

20-lmtp.conf : mail_plugins = $mail_plugins sieve


If the above are the correct settings, why do I get the following 
errors?

Mar 23 00:55:31 host dovecot: lmtp(328): Debug: Module loaded: 
/usr/lib/dovecot/modules/lib10_quota_plugin.so
Mar 23 00:55:31 host dovecot: lmtp(328): Error: 
dlopen(/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so) failed: 
/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so: undefined symbol: 
command_unregister
Mar 23 00:55:31 host dovecot: lmtp(328): Fatal: Couldn't load required plugins

--

Re: quota setup assistance (postfix+dovecot+mysql)

[Gedalya]

On 03/23/2015 06:24 PM, rooster wrote:

On 2015-03-23, at 1:43 AM, Gedalya  wrote:

The imap_quota plugin is relevant only under protocol imap {}. It reports quota 
usage via the IMAP protocol. Under lmtp and any other protocol that can change 
quota usage, you need to load only the quota plugin, which does the actual work 
of accounting and enforcing the quota.


Thank you for the hint. So what I need to do is remove $mail_plugins from 
each "mail_plugins =“ (I think the information I found was wrong in using 
$mail_plugins on each mail_plugins =, based on what you said above)
That idea is to set the global mail_plugins to contain the plugins you 
would want enabled in *all* places. If there is not a single such 
plugin, then indeed you can set the global mail_plugins to empty, but 
then you should still use $mail_plugins everywhere because then it would 
just work, should you ever add a plugin to the global list.



  , and only set the correct corresponding mail plugins? Is my example below, 
correct?

e.g. :

protocol imap {
mail_plugins = zlib quota imap_quota imap_zlib antispam
}

protocol lmtp {
mail_plugins = zlib quota
}

protocol lda {
mail_plugins =
I don't see why you shouldn't add quota here, and zlib too in your case. 
If you don't use lda at all, it still won't hurt.



}

--


Finally, doveadm is sort of a "protocol" too and any protocol for which 
you did not specify its own "mail_plugins = ..." will use the global 
value itself.
So for example here you explicitly turned off all plugins for lda, 
overriding the global value. And doveadm will use the global value. So 
just take it all into consideration.

Re: quota setup assistance (postfix+dovecot+mysql)

[rooster]

> On 2015-03-23, at 1:43 AM, Gedalya  wrote:
> 
> The imap_quota plugin is relevant only under protocol imap {}. It reports 
> quota usage via the IMAP protocol. Under lmtp and any other protocol that can 
> change quota usage, you need to load only the quota plugin, which does the 
> actual work of accounting and enforcing the quota.


Thank you for the hint. So what I need to do is remove $mail_plugins 
from each "mail_plugins =“ (I think the information I found was wrong in using 
$mail_plugins on each mail_plugins =, based on what you said above) , and only 
set the correct corresponding mail plugins? Is my example below, correct?

e.g. :

protocol imap {
mail_plugins = zlib quota imap_quota imap_zlib antispam
}

protocol lmtp {
mail_plugins = zlib quota
}

protocol lda {
mail_plugins =
}

--

Re: [PATCH] [dovecot 2.2.9] Quota warnings ignored with FS quotas

[Michał Giżyński]

On 17.02.2015 20:03, Michał Giżyński wrote:


On 21.11.2014 20:04, Grzegorz Nosek wrote:

Hi all,

I noticed that in some circumstances quota warnings are ignored. The 
bug arises when both of the following are used:


1. percentage-based quota warnings, i.e.:

  quota_warning = storage=1%% quota-warning 1 %u

2. filesystem quota backend (and probably others, except for quotas 
configured directly in dovecot config)


Percentage-based quota warnings have rule.bytes_limit recalculated 
based on root_set->default_rule.bytes_limit, however this value is 
zero when FS quotas are in use. Real quota values (from quotactl) are 
fetched very late, in quota_warnings_execute() but at that point no 
recalculation happens. As the warning rules have bytes_limit==0, 
they're effectively ignored.


The patch below enables quota warnings to be sent when using 
filesystem (and possibly maildirsize-based) quotas.


Based and tested on Ubuntu 14.04's dovecot 2.2.9.

Best regards,
 Grzegorz Nosek


diff --git a/src/plugins/quota/quota.c b/src/plugins/quota/quota.c
index adbd70d..8e4d7e0 100644
--- a/src/plugins/quota/quota.c
+++ b/src/plugins/quota/quota.c
@@ -1163,6 +1163,8 @@ static void quota_warnings_execute(struct 
quota_transaction_context *ctx,

   &count_current, &count_limit) < 0)
return;

+   quota_root_recalculate_relative_rules(root->set, bytes_limit, 
count_limit);

+
bytes_before = bytes_current - ctx->bytes_used;
count_before = count_current - ctx->count_used;
for (i = 0; i < count; i++) {

Hi,
this patch realy fix the bug in quota_warning. Is it possible to add 
this patch to the next release ?



Hi,
I saw that new dovecot was released. Is the quota_warning has been 
improved ?


--
Pozdrawiam / Best Regards
Michał Giżyński

Re: Dovecot Oy merger with Open-Xchange AG

[Patrick Coffin]

To Timo and the Dovecot guys - congratulations!  I'm sure this merger with 
OpenXchange is going to provide you with a lot of resources and opportunities.

As a longtime user of dovecot, I do have a few concerns.  I wonder if you can 
answer some questions for me.

You say that OpenXchange really likes open source and shares your plans for the 
future.  Is this a commitment that future versions core dovecot product will 
remain free and truly open source? 

According to Wikipedia (http://en.wikipedia.org/wiki/Open-Xchange#Licensing 
) , OpenXchange's backend 
is GPL'd, but the front-end is not - it's released under "Creative Common's 
Share Alike, Non Commercial, Attribution".  The article points out: 
 "The restriction to Non Commercial in the Creative Commons license for the 
Frontend restricts re-distribution to third parties, i.e. hosted deployments 
for third parties. However, since the front-end license prohibits commercial 
re-distribution, the software is neither free software nor open source software 
since the definitions of both require such re-distribution to be permitted"

Do you expect that dovecot is moving in that direction?

Here's why I'm asking:  As a hosted email provider, I've long used dovecot, and 
been quite happy with it.  But I have some concerns, as is common when any 
popular open source project gets acquired by a commercial entitiy.

The current dovecot license is a mixture of the MIT and LGPL licenses.  Will 
this remain?  Or is dovecot going to go the way of OpenXchange licensing?   

What about other pieces of the dovecot ecosystem, such as the Object Storage 
plugin - will that remain closed source and proprietary?  Or will you follow 
the lead of companies like RedHat and be truly open source? 

Is there a possibility that future versions of dovecot that contain what we 
might consider core features will be available only in the commercial version 
of the product?

If I base a part of my business on a piece of software I've been running for 
the last 10 years, am I going to find myself in trouble in a year or two, when 
some new version of dovecot comes out with changes that I need, and I have to 
move to a commercial product, which I may or may not be able to afford?

I'd love to hear that you're going to be following a model like RedHat did when 
they acquired GlusterFS and created the RedHat Storage Server.  Gluster 
development is still going strong, and still completely open source.  But they 
make money from people like me who know that by buying a contract, we can get 
the kind of support we need for such a critical part of our infrastructure.

Again, congratulations and, as always, thanks for all the hard work creating 
dovecot in the first place.

Patrick

Re: Dovecot Oy merger with Open-Xchange AG

[Philipp]

Am 23.03.2015 15:08 schrieb Andreas Kasenides:

I am usually emotionally (at least) against of open-source projects
loosing their independence to large corporations. Possibly due to bad
experiences in the past when OSS were driven from Open to Obscure in
the process of trying to make money out of them.


2ct from me--

I put it this way: if dovecot would have been a "pure" OSS before 
getting bought

OAX, then response might would've been different.

But Dovecot OY is "making money out of it" for how long now? Five years 
- and

that's not only "selling support".
Nginx went the same path - I'd say even more aggressive, given feature 
set differences.


Timo and his team has shown that they care about their OSS tree, e.g. do 
you
really think all that replication and director "stuff" came from pure 
boredom?

Show me OSS for cyrus, courier, .. on that level of "enterprisey".

Timo clearly wrote that this company merge is about putting together the
PAID services efforts (think hotlines and such) and not mangling OX and 
dovecot
into some "blob" (well, might happen one day in the future, but you 
would never

know about *any* OSS unless you find a crystal globe telling you).

If my customers are reluctant to move IMAP servers to dovecot, because 
for now
they have/had OX+whatever.. well, what better argument could one have 
then:

Did you know that they are one company and have shared support now? ..

Just thinkin' and sayin'.

Re: Dovecot Oy merger with Open-Xchange AG

[Adrian Zaugg]

I think everyone shares your concerns. But there are no rules that the
outcome of this merger must get something bad, so let's see what
happens. I hope that it's true what Timo said and that dovecot can
evolve and get even better as it is today. Good luck guys!

Regards, Adrian.

On 23.03.15 15:08, Andreas Kasenides wrote:
> I find it extremely interesting that no one has commented on the merger
> of Dovecot Oy and Open-Xchange AG as announced by Timo on the 19th. Is
> this something that was known a long time ago and I missed? OK checked
> the on-line archive of the mailing list, no comments there - its not my
> email set-up - LOL.
> I am usually emotionally (at least) against of open-source projects
> loosing their independence to large corporations. Possibly due to bad
> experiences in the past when OSS were driven from Open to Obscure in the
> process of trying to make money out of them. I have several examples in
> mind but I will not give names. At least that is the impression I have
> which might be entirely wrong since when big companies begin to ask for
> large sums of money we just have to move away due to the small budget.
> Anyway this is not to about judging the move. Which I cannot do since I
> have no knowledge whatsover of the Dovecot enterprise internals and the
> difficulties that come with managing a leading software product. And,
> secondly, since I am (my employer ie) a non paying customer!!
> I was just struck by the fact that no one has commented on it.
> 
> I wish Dovecot the best in the new environment.
> 
> Andreas
> 
> On 19/03/15 12:26, Timo Sirainen wrote:
>> Hi all,
>>
>> Today I can finally announce that Dovecot Oy company has merged with
>> Open-Xchange AG. This helps us to get more Dovecot developers, support
>> people and so on. Most importantly, eventually it should allow me to
>> get back to doing what I like the most: Designing new and interesting
>> stuff for Dovecot and perfecting the old stuff :) OX is a great match
>> to Dovecot going forward. They also really like open source and share
>> our plans for the future. Nothing big will change as a result of this
>> merger: Dovecot will stay Dovecot with its own name and release
>> schedules. We're not going to force OX and Dovecot to be the same
>> product, other than having a somewhat deeper integration between them.
>>
>> Here are the press release links about it:
>> http://www.dovecot.fi/open-xchange-and-dovecot-announce-merger-to-create-worlds-leading-open-source-messaging-software-provider/
>>
>> http://www.open-xchange.com/dovecot
>> http://www.open-xchange.com/announcements/18
> 
> 

Re: Dovecot Oy merger with Open-Xchange AG

[Andreas Kasenides]

I find it extremely interesting that no one has commented on the merger 
of Dovecot Oy and Open-Xchange AG as announced by Timo on the 19th. Is 
this something that was known a long time ago and I missed? OK checked 
the on-line archive of the mailing list, no comments there - its not my 
email set-up - LOL.
I am usually emotionally (at least) against of open-source projects 
loosing their independence to large corporations. Possibly due to bad 
experiences in the past when OSS were driven from Open to Obscure in the 
process of trying to make money out of them. I have several examples in 
mind but I will not give names. At least that is the impression I have 
which might be entirely wrong since when big companies begin to ask for 
large sums of money we just have to move away due to the small budget.
Anyway this is not to about judging the move. Which I cannot do since I 
have no knowledge whatsover of the Dovecot enterprise internals and the 
difficulties that come with managing a leading software product. And, 
secondly, since I am (my employer ie) a non paying customer!!

I was just struck by the fact that no one has commented on it.

I wish Dovecot the best in the new environment.

Andreas

On 19/03/15 12:26, Timo Sirainen wrote:

Hi all,

Today I can finally announce that Dovecot Oy company has merged with 
Open-Xchange AG. This helps us to get more Dovecot developers, support people 
and so on. Most importantly, eventually it should allow me to get back to doing 
what I like the most: Designing new and interesting stuff for Dovecot and 
perfecting the old stuff :) OX is a great match to Dovecot going forward. They 
also really like open source and share our plans for the future. Nothing big 
will change as a result of this merger: Dovecot will stay Dovecot with its own 
name and release schedules. We're not going to force OX and Dovecot to be the 
same product, other than having a somewhat deeper integration between them.

Here are the press release links about it:
http://www.dovecot.fi/open-xchange-and-dovecot-announce-merger-to-create-worlds-leading-open-source-messaging-software-provider/
http://www.open-xchange.com/dovecot
http://www.open-xchange.com/announcements/18



--
Andreas Kasenides
Senior IT Officer
Dept. of Computer Science,
University of Cyprus
Tel: 22892714, Fax: 22892701
(5B4ANK)

Re: Fixing broken UTF-8 handling with MySQL driver

[Felix Zandanel]

> Am 12.03.2015 um 14:55 schrieb Timo Sirainen :
> 
> On 11 Mar 2015, at 21:31, Felix Zandanel  wrote:
>> 
>> Although my MySQL installation is set up to use UTF-8 as the default charset 
>> on every level (config, database, table and field), and the character_set_* 
>> runtime variables all yield the value "utf8", it still seems that the mysql 
>> client library must be instructed to actually use UTF-8 explicitly. Adding 
>> the following statement to driver_mysql_connect() fixes the issue for me:
>> 
>> mysql_options(db->mysql, MYSQL_SET_CHARSET_NAME, "utf8");
> 
> I think you can also add to /etc/my.cnf :
> 
> [client]
> default-character-set = utf8

Sorry for the late reply. You were so right, that simple line did the trick. My 
fault, I didn't read the whole charset documentation of MySQL. It's a shame 
that UTF-8 isn't the default setting.

Anyway, as dovecot's internals expect all input strings to be UTF-8, wouldn't 
it be useful to enforce UTF-8 in the database drivers? Using anything else than 
ASCII / UTF-8 for dovecot's MySQL connections doesn't really make sense, I 
think. Also, a "default-character-set = utf8" line in my.cnf is a system wide 
configuration, which might break other software interacting with MySQL—in 
theory.




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Re: [PATCH] increase fd_limit to max_client_limit automatically

[Lauri Tirkkonen]

On Fri, Mar 20 2015 21:06:12 +0200, Timo Sirainen wrote:
> On 22 Jan 2015, at 14:01, Lauri Tirkkonen  wrote:
> > 
> > Hi, with a low soft limit on file descriptors, dovecot 2.2.15 warns on
> > startup:
> > 
> >Warning: fd limit (ulimit -n) is lower than required under max. load
> >(256 < 1000), because of default_client_limit
> > 
> > It could try increasing the limit first, and only report the warning if that
> > fails. I'm attaching a patch that does just this.
> 
> It could .. But somehow it doesn't seem like a good idea to me to do
> automatically. Maybe the limits are there intentionally.

I would make the argument that that's why there are both soft and hard
limits. Any program can raise their soft ulimits to the current hard
limit - I see the soft limit as more of a guard against misconfiguration
than a resource control, so I don't think there is anything wrong with
raising it when you have a legitimate reason to do so. On systems with
low default fd limits (such as some illumos distributions; see
https://www.illumos.org/issues/3772), the alternative is requiring
administrators to create startup wrappers for dovecot that raise the
limit, but since it's not a privileged operation that just seems silly.

-- 
Lauri Tirkkonen
Niksula systems specialist

Re: quota setup assistance (postfix+dovecot+mysql)

[Gedalya]

On 03/23/2015 04:34 AM, rooster wrote:

Hello list,

I have been struggling with establishing a working installation of 
dovecot with mySQL quota support. I have not been able to find a guide or 
tutorial that works for the current revisions of software I have at my disposal.

Most notably, the error I see in the mail log is as follows :

Mar 23 00:55:31 host dovecot: lmtp(328): Debug: Module loaded: 
/usr/lib/dovecot/modules/lib10_quota_plugin.so
Mar 23 00:55:31 host dovecot: lmtp(328): Error: 
dlopen(/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so) failed: 
/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so: undefined symbol: 
command_unregister
Mar 23 00:55:31 host dovecot: lmtp(328): Fatal: Couldn't load required plugins

I have attached my dovecot -n output. The installed revision of dovecot 
is 2.2.9 on ubuntu 14.04.02 LTS.

Thank you in advance.

--



The imap_quota plugin is relevant only under protocol imap {}. It 
reports quota usage via the IMAP protocol. Under lmtp and any other 
protocol that can change quota usage, you need to load only the quota 
plugin, which does the actual work of accounting and enforcing the quota.

Re: fast doveadm search results

[Vu Ngoc VU]

Hello Timo, thanks you so much for answering.


Date: Fri, 20 Mar 2015 19:16:55
From: Timo Sirainen 

On 20 Mar 2015, at 10:37, Vu Ngoc VU  wrote:


But to answer your questions, I'm not really interested in purging the cache 
data.
I just think that cache has expiration delay.
The only point is to get this "doveadm search" answering me in minutes instead 
of hours.
Writing my original post, I didn't get if it was slow because of:
- data I'm searching are not cached at all? (headers like From, Date, 
Message-ID...)
=> I wanted to know if dovecot allows to add some headers.
Stephen answered to that question.


By default all headers are added to cache the first time they're accessed in 
the folder (e.g. via FETCH or SEARCH). Also mails that are newly delivered by 
Dovecot will add those headers to cache immediately.


Wow, I'm wondering how Dovecot manages to know if it is 1st time access.
So, no matter if it is from a MUA or with dovecot's administrative commands 
like doveadm search/fetch ?
Yes, delivery is done by dovecot LMTP on a separated server, I plan to move 
this service into others servers that do imap/pop3.


- these data a cache, but for an extremely short time, like the user session
=> that's why I asked if it is possible to extend cache validity to at least 
48h.
But for sure, if these data remain forever, it'll be better ! :)


Dovecot automatically figures out if the data should stay in cache for 1 week 
or forever. It sounds like something's wrong in your system if it's not already 
automatically performing fast searches. The first time a search on a header is 
done it might be slow if the data isn't in cache, but all subsequent times 
should be very fast. Not hours or minutes but seconds. No need to modify the 
mail_cache_* settings. It might be helpful if you posted your whole doveconf -n 
output.


I've read on the website and you confirmed here that dovecot tries to be smart 
about how to manage the cache.
But is there settings so I can ask dovecot to never remove cache entries?
I don't want dovecot to try to evaluate if the MUA needs/asks these data often.
Like I wrote before, I host mails for nearly 10 companies inside a same "group" 
(sorry, english is not my native language).
And mails is a tool overused here, so even if it is rare cases, sometimes, they 
ask me to delete some mails quickly.
Then, I prefer to waste some I/O and disk usage for the cache (or indexes, 
whatever it is called) to have doveadm search answer fast.

If there is no "never_purge_cache" or "dont_try_to_be_smart" setting, would it 
be some command to run every night with CRON to update/refill the cache?


- NFS limitations
=> do I have to re-install dovecot on my NFS servers? I prefer not.


What do you mean by this? You're using NFS now to store emails but with one 
Dovecot server? That should work fine, although NFS of course always adds some 
extra overhead.


I can paste configuration somewhere, but since I have several servers, maybe we 
should decide which ones to run `doveconf -n` from.
My setup looks like this, I know there are some design errors:
- storage bays from DELL (MD1220) with 24 hdd, directly SAS attached to some 
physical servers
- these servers attached to the storage bays are NFS servers
- 2 openvz containers running dovecot as director proxy + postfix submission (I 
called these mailhubs)
- 2 openvz containers running dovecot as IMAP/POP3 backends, they are nfs 
clients to access mailboxes
- 1 openvz container acting as MX with postfix and the only one that has 
public+private ip addresses
this server only receives mails for our domains and then "transports" to lmtp 
servers.
It is not part of Director setup.
- 1 openvz container called lmtp, this one is nfs client too, and only delivers 
mails
This one only do delivery and is not part of Director setup, I plan to remove it from the 
"archi".

All systems are Ubuntu 14.04 (so it's dovecot 2.2.9 via packages) and 
filesystem on storage servers is ext4 on hardware RAID-6.

I need to migrate others domains hosted on older setup (with Courier). But before that, I 
prefer having my "new setup" working as expected.
And I also want to understand important parts (for me) like caching of messages. 
To enhance searching performance, I can consider many solutions like integrating SSD, storing indexes/caches in some memcached (we can put 1 TB of RAM on our servers).

But, for now, I need to know if I can configure dovecot so that it add headers 
I need to the cache and never remove these.

I'll do further tests. But for the moment, I've tried this:
- delete dovecot.index.cache file for a mailbox
- running doveadm search on it and check contents of the new cache file with 
strings command
=> only headers I ask in search command are stored
- running another search with another header as criteria
=> the cache file now has stored new asked headers.

As you wrote that on delivery "all" headers should be stored in cache, I'll do 
some tests on this today.

quota setup assistance (postfix+dovecot+mysql)

[rooster]

Hello list,

I have been struggling with establishing a working installation of 
dovecot with mySQL quota support. I have not been able to find a guide or 
tutorial that works for the current revisions of software I have at my disposal.

Most notably, the error I see in the mail log is as follows :

Mar 23 00:55:31 host dovecot: lmtp(328): Debug: Module loaded: 
/usr/lib/dovecot/modules/lib10_quota_plugin.so
Mar 23 00:55:31 host dovecot: lmtp(328): Error: 
dlopen(/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so) failed: 
/usr/lib/dovecot/modules/lib11_imap_quota_plugin.so: undefined symbol: 
command_unregister
Mar 23 00:55:31 host dovecot: lmtp(328): Fatal: Couldn't load required plugins

I have attached my dovecot -n output. The installed revision of dovecot 
is 2.2.9 on ubuntu 14.04.02 LTS.

Thank you in advance.

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# 2.2.9: /etc/dovecot/dovecot.conf
# OS: Linux 3.13.0-45 Ubuntu 14.04.2 LTS ext4
auth_debug = yes
auth_debug_passwords = yes
auth_mechanisms = plain login
auth_verbose = yes
first_valid_gid = 8
first_valid_uid = 8
lda_mailbox_autocreate = yes
lda_mailbox_autosubscribe = yes
listen = *
lmtp_rcpt_check_quota = yes
mail_debug = yes
mail_gid = mail
mail_location = maildir:/var/mail/vmail/%d/%n
mail_plugins = " zlib quota imap_zlib imap_quota antispam"
mail_privileged_group = mail
mail_uid = mail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character 
vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy 
include variables body enotify environment mailbox date ihave
namespace {
  inbox = yes
  location = 
  mailbox {
auto = subscribe
special_use = \Archive
name = Archive
  }
  mailbox {
auto = subscribe
special_use = \Drafts
name = Drafts
  }
  mailbox {
auto = subscribe
special_use = \Junk
name = Junk
  }
  mailbox {
auto = subscribe
special_use = \Sent
name = Sent
  }
  mailbox {
auto = subscribe
special_use = \Trash
name = Trash
  }
  prefix = 
  name = inbox
}
passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
plugin {
  quota = maildir:User quota
  quota_exceeded_message = Sorry, this mailbox is full, please try again later
  quota_grace = 10%%
  quota_rule2 = Junk:ignore
  quota_rule3 = Trash:storage=+100M
  sieve = ~/.dovecot.sieve
  sieve_dir = ~/sieve
  zlib_save = gz
  zlib_save_level = 6
}
postmaster_address = postmaster@%d
protocols = imap lmtp
quota_full_tempfail = yes
rejection_reason = Your message to <%t> was automatically rejected :%n%n%r%n%n
rejection_subject = Rejected : %s
service replication-notify-fifo {
  name = aggregator
}
service anvil-auth-penalty {
  name = anvil
}
service auth-worker {
  user = vmail
  name = auth-worker
}
service {
  unix_listener {
group = postfix
mode = 0666
user = postfix
path = /var/spool/postfix/private/auth
  }
  unix_listener {
mode = 0600
user = vmail
path = auth-userdb
  }
  user = dovecot
  name = auth
}
service config {
  name = config
}
service dict {
  name = dict
}
service login/proxy-notify {
  name = director
}
service dns-client {
  name = dns_client
}
service doveadm-server {
  name = doveadm
}
service {
  inet_listener {
port = 0
name = imap
  }
  name = imap-login
}
service imap-urlauth {
  name = imap-urlauth-login
}
service imap-urlauth-worker {
  name = imap-urlauth-worker
}
service token-login/imap-urlauth {
  name = imap-urlauth
}
service login/imap {
  name = imap
}
service indexer-worker {
  name = indexer-worker
}
service indexer {
  name = indexer
}
service ipc {
  name = ipc
}
service {
  unix_listener {
group = postfix
mode = 0600
user = postfix
path = /var/spool/postfix/private/dovecot-lmtp
  }
  user = mail
  name = lmtp
}
service log-errors {
  name = log
}
service sieve {
  name = managesieve-login
}
service login/sieve {
  name = managesieve
}
service pop3 {
  name = pop3-login
}
service login/pop3 {
  name = pop3
}
service replicator-doveadm {
  name = replicator
}
service login/ssl-params {
  name = ssl-params
}
service stats-mail {
  name = stats
}
ssl = required
ssl_cert =