readonly archive folders using squashfs

[Yassine Chaouche]

For every user at domain.tld I created a user at backup.domain.tld where he 
could look up deleted messages (archive).

I then made user at backup.domain.tld's cur directory a shared directory to 
user at domain.tld but only with read privileges. So, anytime the user 
wants to read his old messages, he only needs to read his .archive 
folder, which is user at backup.domain.tld's cur. No need to make the 
filesystem read-only.

The difficulty is to make sure that every e-mail, sent or received, gets 
backed up properly before being deleted. Relying on cron jobs is not an 
option since the e-mail can be deleted and expunged before the script 
has a chance to get executed and do the backup. So what I did is to 
create a hidden sieve filter for every user's **main** mailbox 
(user at domain.tld) that automatically creates a copy of every incoming 
message to the user at backup.domain.tld mailbox. For outgoing e-mail, one 
can do a bcc map in postfix (or the equivalent in other SMTP software) 
that ensures that every sent mail is also sent to 
user+sent at backup.domain.tld, then you can create a filter in the user's 
**backup** mailbox (user at backup.domain.tld) that filters on the 
user+sent part of the e-mail and stores every e-mail sent to that e-mail 
address to the .Sent directory in the user at backup.domain.tld mailbox.


Finally, the backup.domain.tld doesn't even have to be declared in the 
DNS nor in /etc/hosts and can be entirely virtual to the MTA (for ex. in 
postfix that would only be added to virtual_mailbox_domains)

Yassine.

On 3/8/19 12:49 AM, Natu via dovecot wrote:
> I have a dovecot server running under CentOS using maildir format.  Due
> to the issue with minimum blocksize for files I would like to offer some
> kind of readonly archive using something like the compressed squashfs
> where I would move messages to be archived to a maildir folder and then
> convert "cur" directory into a squashfs and mount it in place of the
> original directory so my biggest users could have readonly access to
> older messages without it using so much disk space.
>
> Has anyone tried anything like this before and is dovecot likely to
> complain about the readonly cur directory?  If the complaints are
> minimal and didn't cause other problems it might be ok.  Any better
> ideas to implement something like this?
>
> Thank You,
>
> Natu
>
>