Background:

Shared folders allow email clients to share folders for certain purposes. For example, I am going to set up a shared junk-mail folder to allow my users to check for incorrectly flagged junk mail.

Shared folders is described in the latest imap standard, but unfortunatly outlook express does not support them very well. At the time of this writing, my clients will be able to use sqwebmail or thunderbird (by the makers of mozilla) to access shared folders. Users not needing to view the shared folder can still use outlook express.

I should also mention that shared-folders are not ment to have mail delivered to them directly. They were ment to allow users to transfer messages into them for sharing. This is done for security purposes, but sometimes too much security is just annoying, so there if you are using maildrop to deliver your mail, there is a workaround listed below.

First, read the manpage for maildirmake, specifically the section for shared folders. Here are the highlights.

A user wishing to create a shared folder will need to do the following:

To create a sharable maidir:

maildirmake -S [path_of_maildir]

To create a sharable folder within a maildir:

maildirmake -s read -f [new_folder_name] [path_of_maildir]

A user wishing to access another person's shared maildir will need to do the following:

maildirmake --add [folder_alias]=[path_of_shared_maildir] [path_of_my_maildir]

Morphing a maildir to a shared-maildir:

In my case, I just wanted to share a folder in my own maildir with a few other users. (which is also not recommended for security purposes) I simply created a shared folder, and watched to see what maildirmake set on the shared folder. Then I applied those changes manually to my junk-mail folder.

Shared-maildirs need to be chmod 755 from the root all the way to the shared folder. The messages within the shared folder must be chmod 644.

chmod 755 $HOME/Maildir

find $HOME/Maildir/.Junk\ Mail -type d -exec chmod 755 {} \;
find $HOME/Maildir/.Junk\ Mail -type f -exec chmod 644 {} \;

Normally, my clients would then have to log into my server and run the maildirmake --add command in order to access my shared folder. Since my clients do not have permission to log into my server, I will do this for them.

cd [client-maildir]

add the following line to the file 'shared-maildirs':

Shared-Maildir Delivery Issues

I use blackhole to flag my spam, then I use maildrop to deliver it to my junk-mail folder. The bad news is, maildrop always delivers mail with permissions 600, which means that our clients will not be able to view any freshly delivered messages. There is no way around this without modifying the rule that delivers mail to the junk-mail folder. Since I let my users access their maildrop filter via sqwebmail, and sqwebmail does not support changing default delivery permissions, this must be done by me as root. The good news is that it is just a simple rule change, and not a software hack that must be re-applied after every update.

The old rule:

##Op:startswith
##Header:subject
##Value:SPAM:
##Folder:.Junk Mail
##From:
##PlainString
##Name:BlackHole JunkMail

if ((/^subject: *SPAM\:/))
{
to "./Maildir/.Junk Mail/."
}

The new rule:

##Op:startswith
##Header:subject
##Value:SPAM:
##Folder:.Junk Mail
##From:
##PlainString
##Name:BlackHole JunkMail

if ((/^subject: *SPAM\:/))
{
UMASK="033"
to "./Maildir/.Junk Mail/."
}