This is the README file for mail500, a mailer that does X.500 lookups
via LDAP.

If you are planning to run mail500 at your site, there are several
things you will have to tailor in main.c:

	LDAPHOST - The host running an LDAP server

	base[] - The array telling mail500 where/how to search for
		things.  See the explanation below.

*** WHAT mail500 DOES: ***

mail500 is designed to be invoked as a mailer (e.g., from sendmail),
similar to the way /bin/mail works.  It takes a few required arguments
and then a list of addresses to deliver to.  It expects to find the
message to deliver on its standard input.  It looks up the addresses in
X.500 to figure out where to route the mail, and then execs sendmail to
do the actual delivery.  It supports simple aliases, groups, and
mailing lists, the details of which are given below.

*** HOW IT WORKS (from the sendmail side): ***

The idea is that you might have a rule like this in your sendmail.cf
file somewhere in rule set 0:

R$*<@umich.edu>$*	$#mail500$@umich.edu$:<$1>

This rule says that any address that ends in @umich.edu will cause
the mail500 mailer to be called to deliver the mail.  You probably
also want to do something to prevent addresses like terminator!tim@umich.edu
or tim%terminator.rs.itd.umich.edu@umich.edu from being passed to mail500.
At U-M, we do this by adding rules like this to rule set 9 where we
strip off our local names:

R<@umich.edu>$*:$*                 $>10<@>$1:$2
R$+%$+<@umich.edu>                 $>10$1%$2<@>
R$+!$+<@umich.edu>                 $>10$1!$2<@>

See the sample sendmail.cf in this directory for more details.

The mail500 mailer should be defined similar to this in the
sendmail.cf file:

Mmail500, P=/usr/local/etc/mail500, F=DFMSmnXuh, A=mail500 -f $f -h $h -m $n@$w $u

This defines how mail500 will be treated by sendmail and what
arguments it will have when it's called.  The various flags specified
by the F=... parameter are explained in your local sendmail book (with
any luck).  The arguments to mail500 are as follows:

	-f	Who the mail is from.  This will be used as the address
		to which any errors should be sent (unless the address
		specifies a mailing list - see below).  Normally, sendmail
		defines the $f macro to be the sender.

	-h	The domain for which the mail is destined.  This is passed
		in to mail500 via the $h macro, which is set by the
		$@ metasymbol in the rule added to rule set 0 above.
		It's normally used when searching for groups.

	-m	The mailer-daemon address.  If errors have to be sent,
		this is the address they will come from.  $n is normally
		set to mailer-daemon and $w is normally the local host
		name.

The final argument $u is used to stand for the addresses to which to
deliver the mail.

*** HOW IT WORKS (from the mail500 side): ***

When mail500 gets invoked with one or more names to which to
deliver mail, it searches for each name in X.500.  Where it searches,
and what kind(s) of search(es) it does are compile-time configurable
by changing the base array in main.c.  For example, the configuration
we use at U-M is like this:

	Base    base[] =
		{ "ou=People, o=University of Michigan, c=US", 0
			"uid=%s", "cn=%s", NULL,
		  "ou=System Groups, ou=Groups, o=University of Michigan, c=US", 1
			"(&(cn=%s)(associatedDomain=%h))", NULL, NULL,
		  "ou=User Groups, ou=Groups, o=University of Michigan, c=US", 1
			"(&(cn=%s)(associatedDomain=%h))", NULL, NULL,
		  NULL
		};

which means that in delivering mail to "name" mail500 would do the
the following searches, stopping if it found anything at any step:

	Search (18) [2]: c=US@o=University of Michigan@ou=People
	Search subtree (uid=name)
	Search (18) [3]: c=US@o=University of Michigan@ou=People
	Search subtree (cn=name)

	Search (18) [4]: c=US@o=University of Michigan@ou=Groups@ou=System Groups
	Search subtree & ((cn=name)(associatedDomain=umich.edu))

	Search (18) [5]: c=US@o=University of Michigan@ou=Groups@ou=User Groups
	Search subtree & ((cn=name)(associatedDomain=umich.edu))

Notice that when specifying a filter %s is replaced by the name,
or user portion of the address while %h is replaced by whatever is
passed in to mail500 via the -h option (typically the host portion
of the address).

You can also specify whether you want search results that matched
because the entry's RDN matched the search to be given preference
or not.  At U-M, we only give such preference in the mail group
portion of the searches.  Beware with this option:  the algorithm
used to decide whether an entry's RDN matched the search is very
simple-minded, and may not always be correct.

There is currently no limit on the number of areas searched (the base
array can be as large as you want), and an arbitrary limit of 2 filters
for each base.  If you want more than that, simply changing the 3 in
the typedef for Base should do the trick.

*** HOW IT WORKS (from the X.500 side): ***

In X.500, there are several new attribute types and one new object
class defined that mail500 makes use of.  At its most basic, for normal
entries mail500 will deliver to the value(s) listed in the
rfc822Mailbox attribute of the entry.  For example, at U-M my entry has
the attribute

	mail= tim@terminator.rs.itd.umich.edu

So mail sent to tim@umich.edu will be delivered via mail500 to that
address.  If there were multiple values for the mail attribute, multiple
copies of the mail would be sent.

A new object class, rfc822MailGroup, and several new attributes have
been defined to handle email groups/mailing lists.  To use this, you
will need to add this to your local oidtable.oc:

	# object class for representing rfc 822 mailgroups
	rfc822MailGroup:        umichObjectClass.2 : \
		top : \
		cn : \
		rfc822Mailbox, member, memberOfGroup, owner, \
		errorsTo, rfc822ErrorsTo, requestsTo, rfc822RequestsTo,
		joinable, associatedDomain, \
		description, multiLineDescription, \
		userPassword, krbName, \
		telecommunicationAttributeSet, postalAttributeSet

And you will need to add these to your local oidtable.at:

	# attrs for rfc822mailgroups
	multiLineDescription:   umichAttributeType.2    : CaseIgnoreList
	rfc822ErrorsTo:         umichAttributeType.26   : CaseIgnoreIA5String
	rfc822RequestsTo:       umichAttributeType.27   : CaseIgnoreIA5String
	joinable:               umichAttributeType.28   : Boolean
	memberOfGroup:          umichAttributeType.29   : DN
	errorsTo:		umichAttributeType.30	: DN
	requestsTo:		umichAttributeType.31	: DN

The idea was to define a kind of hybrid mail group that could handle
people who were in X.500 or not.  So, for example, members of a group
can be specified via the member attribute (for X.500 members) or the
rfc822MailBox attribute (for non-X.500 members).  Similarly for the
errorsTo and rfc822ErrorsTo, and the requestsTo and rfc822RequestsTo
attributes.

To create a real mailing list, with a list maintainer, all you have to
do is create an rfc822MailGroup and fill in the errorsTo or
rfc822ErrorsTo attributes (or both).  That will cause any errors
encountered when delivering mail to the group to go to the addresses
listed (or X.500 entry via it's mail attribute).

If you fill in the requestsTo or rfc822RequestsTo (or both) attributes,
mail sent to groupname-request will be sent to the addresses listed
there.  mail500 does this automatically, so you don't have to explicitly
add the groupname-request alias to your group.

To allow users to join a group, there is the joinable flag.  If TRUE,
mail500 will search for entries that have a memberOfGroup attribute
equal to the DN of the group, using the same algorithm it used to find
the group in the first place (i.e. the DNs and filters listed in the
base array).  This allows people to join (or subscribe to) a group
without having to modify the group entry directly.  If joinable is
FALSE, the search is not done.

Finally, keep in mind that this is somewhat experimental at the moment.
We are using it in production at U-M, but your mileage may vary...
