dovecot - Oct 2020 - How to move/reorganise existing e-mails to yearly subfolders

Hi all:

I am new to e-mail servers and I am evaluating Dovecot. Not really the best
combination. 8-)

I am trying to find a balance between legal data retention requirements and
online mailbox size. I do not want huge online mailboxes, as doing
offline, rotating data backups could then take forever (among other reasons). I
would rather avoid online (cloud) backups (data protection etc.).

If I set a mailbox size limit, users will have to delete old mails by
themselves. Or I could somehow script the deletion of attachments from old
e-mails, as attachments are usually the main cause of huge mailboxes.
Incidentally, can anyone point me to an easy way to achieve this? Preferably
over with IMAP, otherwise with Dovecot tools.

With regards to legal data retention (which I am no expert about either), I
thought I could use some Postfix BCC feature I heard about in order to
copy all incoming and outgoing e-mails to a single "data retention"
mailbox. Or maybe several of them. I could then archive e-mails from that
mailbox
on a yearly basis.

I would like to automatically organise e-mails inside that mailbox into
subfolders like this:

2019/alice
2019/bob
2020/alice
2020/bob

That is: [year]/[username]

With such a folder structure, it is easier to see what is going on.

Is there a tool that can reorganise existing e-mails into such a folder
structure?

I found some tools on the Internet to backup and export mails from IMAP to IMAP
or maildir destinations. But I could not find a tool that just
reorganises (moves) e-mails in such a manner inside an existing mailbox, maybe
with a user-defined pattern for the destination folders.

I guess moving e-mails around on the same mailbox would be much faster than
exporting and reimporting them in some clever way.

I could always write a Perl script, but that takes time. Such a tool may already
exist. Or perhaps somebody could mention a similar, good-written
script I can use as a starting point. I am sure there are many small gotchas to
avoid. At the moment, I am only confident with Perl and Java. Maybe
JavaScript.

It would be best to reorganise the e-mails over IMAP. This way, I am independent
of the e-mail server. But a Dovecot-specific solution would also be
helpful.

I could use such a reorganisation tool not just for archiving or data retention
purposes, but to reorganise other mailboxes too, like my personal mailbox.

I would rather have a script. Clicking around in Thunderbird does not scale.

I have seen that you can use a "sieve" in Dovecot to achieve this. But
I guess that would only apply to new e-mails. And that would probably apply
just to incoming mails, and not to outgoing ones. If I migrate from the existing
e-mail servers, the e-mails will probably be mass-imported without
going through any "sieve", right?

Besides, I already have a few huge mailboxes with many years of e-mails, stored
in a different e-mail server, and it would be nice to be able to
reorganise them as they are. That way, I could archive the existing older
e-mails before migrating to Dovecot, which would reduce the disk size and
the export/import time for the migration.

Many thanks in advance,
   rdiez

What is the problem with having huge online mailboxes? Just choose a 
good european provider that has encryption all the way through to their 
storage platform.

I had exactly the same idea about migrating. You have to think twice 
about moving emails around of users. They do not like it ;)  I have 
created an 'archive' environment on a distributed filesystem, and it 
takes me quite a lot of persuading to have people (or allow me) to move 
messages from common Sent and Inbox mailboxes to the Archive namespace 
(was not able to use the alternative storage option that dbox allows). 
Side note is that if you do archive these emails, most users do not even 
notice you have done this.

I ended up creating a script and a webmail plugin for users to enable 
autoarchiving, which creates something like this. 

[@~]# mailbox-ls.sh testtest size
listing mailboxes of testtest:
Archive messages=0
Archive/2011 messages=0
Archive/2012 messages=0
Archive/2013 messages=0
Archive/2014 messages=0
Archive/2015 messages=0
Archive/2016 messages=0
Archive/2017 messages=0
Archive/2018 messages=0
Archive/2019 messages=3500
Archive/Archive messages=1
Deleted Messages messages=16
Drafts messages=2
INBOX messages=1286
INBOX/test2 messages=11
Junk messages=2
Sent messages=0
Trash messages=132

A cron job checks then if the script has run for the user this year, if 
not it starts archiving in the down hours otherwise it runs again in 
next year's 2nd quarter. What ever you choose, move messages with 
"doveadm move". I would not trust anyone else's programming with
my
users email, you should also not. Read the man pages on tools that work 
via imap, if they change headers, users are going to download all their 
messages again. I was thinking of splitting up folders like eg 
inbox/sales to Archive/2016/sales, Archive/2017/sales. But when I 
migrate to mdbox this is not necessary anymore.

I do not like the sound of "Postfix BCC feature", I use sendmail and I
can duplicate messages with that, without altering anything in them. You 
do not want anything that changes your data. If your provider uses this 
mdbox format (maybe others support this also) then messages a user 
deletes, are not even removed from the server until "doveadm purge" is
given ;)


 

-----Original Message-----
From: R. Diez [mailto:rdiezmail-2006 at yahoo.de] 
Sent: Monday, October 19, 2020 3:49 PM
To: dovecot at dovecot.org
Subject: How to move/reorganise existing e-mails to yearly subfolders

Hi all:

I am new to e-mail servers and I am evaluating Dovecot. Not really the 
best combination. 8-)

I am trying to find a balance between legal data retention requirements 
and online mailbox size. I do not want huge online mailboxes, as doing 
offline, rotating data backups could then take forever (among other 
reasons). I would rather avoid online (cloud) backups (data protection 
etc.).

If I set a mailbox size limit, users will have to delete old mails by 
themselves. Or I could somehow script the deletion of attachments from 
old e-mails, as attachments are usually the main cause of huge 
mailboxes. Incidentally, can anyone point me to an easy way to achieve 
this? Preferably over with IMAP, otherwise with Dovecot tools.

With regards to legal data retention (which I am no expert about 
either), I thought I could use some Postfix BCC feature I heard about in 
order to copy all incoming and outgoing e-mails to a single "data 
retention" mailbox. Or maybe several of them. I could then archive 
e-mails from that mailbox on a yearly basis.

I would like to automatically organise e-mails inside that mailbox into 
subfolders like this:

2019/alice
2019/bob
2020/alice
2020/bob

That is: [year]/[username]

With such a folder structure, it is easier to see what is going on.

Is there a tool that can reorganise existing e-mails into such a folder 
structure?

I found some tools on the Internet to backup and export mails from IMAP 
to IMAP or maildir destinations. But I could not find a tool that just 
reorganises (moves) e-mails in such a manner inside an existing mailbox, 
maybe with a user-defined pattern for the destination folders.

I guess moving e-mails around on the same mailbox would be much faster 
than exporting and reimporting them in some clever way.

I could always write a Perl script, but that takes time. Such a tool may 
already exist. Or perhaps somebody could mention a similar, good-written 
script I can use as a starting point. I am sure there are many small 
gotchas to avoid. At the moment, I am only confident with Perl and Java. 
Maybe JavaScript.

It would be best to reorganise the e-mails over IMAP. This way, I am 
independent of the e-mail server. But a Dovecot-specific solution would 
also be helpful.

I could use such a reorganisation tool not just for archiving or data 
retention purposes, but to reorganise other mailboxes too, like my 
personal mailbox.

I would rather have a script. Clicking around in Thunderbird does not 
scale.

I have seen that you can use a "sieve" in Dovecot to achieve this. But
I
guess that would only apply to new e-mails. And that would probably 
apply just to incoming mails, and not to outgoing ones. If I migrate 
from the existing e-mail servers, the e-mails will probably be 
mass-imported without going through any "sieve", right?

Besides, I already have a few huge mailboxes with many years of e-mails, 
stored in a different e-mail server, and it would be nice to be able to 
reorganise them as they are. That way, I could archive the existing 
older e-mails before migrating to Dovecot, which would reduce the disk 
size and the export/import time for the migration.

Many thanks in advance,
   rdiez

First of all, thanks for your answer.
> What is the problem with having huge online mailboxes? Just choose a >
good european provider that has encryption all the way through to their>
storage platform.
We already have a European ISP with a standard e-mail server. I wanted to keep
our own mail server on premises, so that it is not exposed on
the Internet. The current server fetches (and removes) all e-mails from the ISP.
That has many advantages, for example, internal e-mail
still works in case of an Internet outage.

If I wanted to change the setup, I would have to start evaluating such an
"encryption all the way through to their storage platform"
feature. I am not sure that it is worth the effort. In any case, that sounds
like a limiting factor when choosing another ISP, in case the
current one starts making trouble.

> I had exactly the same idea about migrating. You have to think twice >
about moving emails around of users. They do not like it ;)
 > [...]

I don't really want to do that, that's why I wrote "If I set a
mailbox size limit, users will have to delete old mails by themselves".

I do not know much about the legal aspects, but in case we need to keep all
e-mails for legal data retention requirements, I would like to
store those e-mails separately, so that if a user deletes it, the original
e-mail is still archived somewhere else.

That is why I mentioned the Postfix's BCC feature. The idea is that you have
a separate mailbox where a separate copy of all e-mails to and
from all users land. That is the separate mailbox where I wanted to reorganise
e-mails by date, in order to archive the e-mails in smaller
chunks on a yearly basis. Those e-mails do not need to be online after all.
Chances are, they will never be needed anyway.

> I have created an 'archive' environment on a distributed
filesystem, and it
> takes me quite a lot of persuading to have people (or allow me) to move
> messages from common Sent and Inbox mailboxes to the Archive namespace
 > [...]

I am actually a newbie in mail service matters, but my guess is that there is no
amount of persuasion that could possibly help. You have to
set a hard limit per mailbox and let the users deal with it, don't you?
Otherwise, sooner or later the server will overload. Or I would need
to become a full-time e-mail server admin, which is not an option either!

I am actually a friend of having 2 backup disks that rotate, where one is always
physically off premises, and offline. But I wonder how I
could keep the backups encrypted and synchronised with 2 rotating disks. Maybe
Veracrypt + rsync.

I am hoping that the amount of big attachments in all incoming and outgoing mail
still fits in normal external USB 3.0 disks. Or at least a
few years' worth of it per disk. But I still would not want to have say 1 TB
of mail data online. That would make the VM unmanageable for
part-time sysadmins like me.

> [@~]# mailbox-ls.sh testtest size
 > [...]
> I would not trust anyone else's programming with my
> users email, you should also not.
I am not sure that I would trust my own e-mail server programming abilities
either. 8-)

If you have written such scripts, perhaps you could point me to some example
scripts that I could use as a starting point for such e-mail
reorganisation tasks?


 > [...]
> But when I migrate to mdbox this is not necessary anymore.
I am not sure that I would trust a file format where the indexes cannot be
rebuilt if they become corrupt. If I need an advanced format for
search performance reasons, I would probably consider an SQL-based backend then.

> I do not like the sound of "Postfix BCC feature", I use sendmail
and I
> can duplicate messages with that, without altering anything in them.
 > [...]

I am actually not sure yet how to achieve the copying. I am still a little
confused anyway. 8-)

On the incoming side, I may not use Postfix at all, because Dovecot actually
needs to download the e-mails from the ISP mail server. I am
hoping that I can use a single "catch all" mailbox on the ISP. So I
would need to copy the incoming e-mails in another way.

On the outgoing side, anything sent (actually per SMTP relay) through our
internal mail server could be copied somehow with some BCC
feature. But if the user connects to the external ISP's SMTP servers
directly, then I cannot get a copy so easily. Maybe I need to force the
users to always use the internal mail server for sending.

In any case, let's say that the duplicate mails, stored somewhere else for
data retention purposes, get altered in some way, like some
header is added or changed in a predictable way. I am thinking of a header like
"BCC: dataretention at example.com". Why would that be a problem?


Best regards,
   rdiez

R. Diez wrote:
> 
> I found some tools on the Internet to backup and export mails from IMAP to
> IMAP or maildir destinations. But I could not find a tool that just
> reorganises (moves) e-mails in such a manner inside an existing mailbox,
> maybe with a user-defined pattern for the destination folders.
You could try imapfilter (written in lua), it can move mails between
mailboxes and do other things.

A short example:

oldmails = account1["INBOX"]:is_older(365)
oldmails:move_messages(account1["Old"])

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
2:5005/49 at fidonet http://vas.tomsk.ru/
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