Produced by the Free Range Salvage Server Project, October 2003
email: fraw@gn.apc.org web: http://www.fraw.org.uk/ssp/
Also available as an Acrobat file (for printing) –
click here.
KMail is a moderately lightweight email client
that works well under both the KDE and Gnome desktops. But it also has very good
mail filtering functions. These can be manipulated to forward mail automatically
each time your mail is checked. So making KMail function as a small email list
server.
This idea started out as solution to a problem – how to create short-term
email lists. There are free list servers available, like Yahoo's egroups.
But you have to accept advertising appended to every mail sent through the list.
You could buy a list on a server, but that costs money, and often it's an
excessive answer when you just want to set up a short-term list to support an
event.
Linux has many facilities to set up mailing lists on your own computer –
although this can be complex if you are not your own ISP. So we need something
far simpler that anyone with a little experience of using email can set up.
The simplest option is to use the features of an existing email program. Whilst
there are many options available, we began experimenting with the mail filtering
functions within KMail to set up simple mail forwarding. The advantage of this
is that you don't have to set up a server. Each time that you check your email
the program will identify mail that is to be forwarded, and then automatically
send it out as your other ordinary mail comes down.
This is not a solution that is acceptable as a replacement for an email list
server. There are two significant flaws. Firstly, it only functions when you
check your mail – forget to check your mail and the messages will not be
relayed. Secondly, if the mail ever bounces the bounces could propagate repeatedly
over the list until you notice the problem and manually remove that address from
the list. Thirdly, there's no facility to archive messages from the list. But,
on the positive side, as a means of setting up a short term list around a
particular event or project, it's far more flexible that using an email list,
or free list service.
Options for identifying lists –
by address or subject
For this system to work you have to have an email address to send mail for
forwarding to. This needs to be different from your ordinary email address.
If you use the same address for everything then mail will just 'feedback'
through the mailbox. You must download mail from the list address, and
forward under the list address. But for you to participate in the list you
have to send under a different address to that of the list.
There are two options:
Have two email addresses (quite common today with most ISPs offering
dial-up email) – which allows multiple forwarding lists if the mail was
identified with a different subject line. If you want more than one list with
this option list uers must correctly type the list name in the subject line
– e.g. '[LIST]'.
For those with a domain name that forwards mail for the domain to their
usual email address, use can any address you like within your domain –
you then filter the email from your ordinary mail.
Of the two, the latter is the best option. This is because each forwarding
list can have a different – albeit non-existent – email address.
Your ISP usually forwards email from the domain to your main email address
– providing the required separation between your email address and the
list address.
Identifying different lists by the subject line requires that people remember
to correctly type the name into the subject line. If this isn't done, the mail
won't forward. You could do without a subject line ID, but that will limit
you to operating only one forwarding list because you can't differentiate
between them.
KMail user IDs
To operate forwarding using KMail you need to set up a user ID for the list
and a mail filter. The purpose of the user ID is to provide an identity for
the email list when KMail forwards mail. If you don't do this then the mail
will be forwarded under your own identity – meaning that any replies will
only go back to you.
From the KMail menu bar, click
Settings, then
Configure KMail,
and if it's not already there, click on the
Identities tab.
To create a new mail ID click
New. In the
New Identity box,
type the name of the forwarding list (see 'a' below).
Clicking 'OK' takes you to the ID configuration dialog box at the
General tab (see
'b' below). Firstly, enter the name of the list in the name box, and the email
address in the address
box. Next to the advanced
tab (see 'c' below). Set the
reply-to address,
which should be the same as the email address. If you wish you can set the
locations where mail will be stored, but this is not necessary as these will
be set via filtering later. You need not set anything in the
signature tab (see
'd' below), so just click OK to set the new identity.
This completes the configuration of the identity. If you use email addresses
from a domain you need to set up one ID for each address. If using a single
address with a subject line ID, you need only set up one ID.
(a)
(c)
(b)
(d)
KMail's mail filters
Mail filters are a time saving means of sorting your email according to who
they're from or dumping obvious spam straight into the trash. But KMail's
filters have powerful features that allow us to re-write the headers of the
email and send it out again.
From the KMail menu bar, click
Settings, then
Configure Filters.
To create a new filter click the
New button at
the bottom left of the dialog box. We'll begin by setting up a domain-based
forwarding list.
To begin, click on the More
button in the Filter Options part of the dialog box. You need seven filter
options – click more until you have seven. Then, in the
Advanced Options
area, uncheck the on manual
filtering and if
filtering matches options – just leave the
to incoming option
checked. This ensures that the filter will only work on downloaded
messages.
Firstly we set the Filter
Criteria. Make sure that Match
all is selected. To filter on the incoming email address we set the
first selection box on the first line to
To. This tests every
To: header on each incoming email to see where it was sent to. The next
selection box should be sets to contains. In the text box we enter the email
address of the email forwarding list – in the example right,
newlist@domain.org.uk. This name must correspond to the email address
given in the KMail ID you set up previously for the list.
Next we set the Filter Actions.
Filtering is a chain of events triggered when the criteria in
Filter Criteria are
met. This could be one action – such as moving the email to a particular
directory. But for email forwarding we have seven actions – one action per
line:
We remove the Reply-to
header from the email. Click on the first selection box and select
remove header. The
next selection box on the line will now change it format. Click on this and select
Reply-to. This will be
set to the email address of the email sender. We remove it to replace it with the
email address of the list.
We change the identity of the outgoing email to that of the list. This ensures
that the Reply-to header on the outgoing email belongs to the list, not the
ordinary KMail client user. Click the first selection box and select
set identity to. The
next box will now contain a list of configured KMail users, and from this box you
select the ID you configured for the forwarding list.
Next we edit the return path to make sure that it doesn't contain the user's
details, but those of the email list. Set the first selection box to
rewrite header. The
second selection box doesn't contain an entry for Return-path and so we
manually type this into the box. Then enter your email address in the first text
box, and the email address of the list in the second.
We rewrite the From: header to ensure that it contains the identity of
the list, changing the user's email address to that of the list. Again, rewrite
header doesn't have and entry for From, so type it into the blank
option. Then enter your usual email address in the first text box and the list
email address in the second.
To complete the rewrite of From:, we change the name from the user's
to that of the list – follow the same procedure as above, but enter the
name KMail uses for your ordinary account in the first box, and the name of the
list in the second.
Now we redirect the email to a list of users. In the first selection box
select redirect to.
You are then given a text box. It is this text box that will contain the list
of people that the email on the list will be sent to. Whenever you need to change
list member details, you have to edit the contents of this box. To check that
the forwarding filter works, you need to include your own address here.
If we do nothing more the email that has been forwarded will be left in
your inbox folder. We conclude by moving to the incoming email to a folder
created to hold the email that has been forwarded to the list.
Clicking OK stores the filter rule. You can now test if it works by
emailing to the list address. Then check your mail. You should notice that
during the mail check the counter for the outbox folder clocks up a
pending mail, and then goes back down again once its sent.
Check your mail again to see if the forwarding filter works. Select
View from the menu
bar, then Headers,
then All Headers.
Now view the email and check the content of the headers. If all's well the
identities in the headers should relate to the list ID, not your main email
ID. The return addresses should also point to the list email address.
If you wish to us a single address, and then filter on an ID in the subject
line, you need to configure the filter rule differently (see box right).
In addition to the Filter
Criteria for the email address, you need to add a second that checks
the subject line for the list ID. Other than this, the
Filter Actions
section carries out the same changes to the content of the mail. But instead
of having a different address for each list, you use the same email address
and have a different filter rule for each of the forwarding lists that you
run through it. The only different between each being the name in the
Filter Criteria
test of the Subject
line, and the content of the redirect
to box.
You will have to completely write the filter rule from scratch each time you
create a new list as there's no copy function for filter rules.
Beware – this is a cheap and easy
hack
This idea has been developed to sole a simple problem – getting a small
automated list to co-ordinate people on-line up and running without having to
resort to a full-blown list server. But it's not without its problems.
As well as the fact it only works when you check your mail, it is particularly
susceptible to bounced mail. But the fact that you manually trigger the
forwarding process when you check mail means that, in between checking mail,
if you check the folder where you move forwarded mails you should easily see
problems when they develop.
The other restriction is that the list is wholly public. Unless you add
additional Filter Criteria to test the From header in each mail,
and only trigger for certain email addresses or domains, then anyone can send
through the list once its address is known. As we can only redirect within
the To: header, not the Bcc: header, it also means that the
distribution list will be mailed each time in the To: header. This
makes it a potential spam liability, and potentially a conduit for viruses
when Windows users are part of the list.
Salvage Server Project Report No.3
For this system to work you have to have an email address to send mail for
forwarding to. This needs to be different from your ordinary email address.
If you use the same address for everything then mail will just 'feedback'
through the mailbox. You must download mail from the list address, and
forward under the list address. But for you to participate in the list you
have to send under a different address to that of the list.
From the KMail menu bar, click
Settings, then
Configure Filters.
To create a new filter click the
New button at
the bottom left of the dialog box. We'll begin by setting up a domain-based
forwarding list.
If you wish to us a single address, and then filter on an ID in the subject
line, you need to configure the filter rule differently (see box right).
In addition to the Filter
Criteria for the email address, you need to add a second that checks
the subject line for the list ID. Other than this, the
Filter Actions
section carries out the same changes to the content of the mail. But instead
of having a different address for each list, you use the same email address
and have a different filter rule for each of the forwarding lists that you
run through it. The only different between each being the name in the
Filter Criteria
test of the Subject
line, and the content of the redirect
to box.