Sample Sendmail Coding

Five basic additions are made to the sendmail.cf configuration file:

1. DLluser ($L (LUSER_RELAY) macro)
2. Sendmail LDAP ``map'' declaration. The LDAP search key and attribute to return are specified with the -k and -v parms:
   

   Kluser ldap
   -h""
   -k"cn=%s" -vmail
   -b"o=,c=US"
   

3. in Ruleset 5, the ``send unrecognized local users to a relay host'' rule is activated and the following rule is added following it, which tells Sendmail to make an LDAP connection and search if the ``local'' user is not found in the server password file/user database (luser is the LDAP ``map'').
   

   R< $L > 	$+ $: < $L > $(luser $1 $)
   

4. in Rulest 98, two rules are added: one for the ``local'' mailing lists, the other for the dotted ``local'' userids:
   

   # look for any (rfc822mailgroup)
   # .mlist, via Mail500
   R$- . mlist <@ $=w .>	 $* $#mail500 $@$2 $: <$1>
   
   # anything like .
   # at  send to MAIL500
   R$- . $- <@ $=w .>	 $* $#mail500 $@$3 $: <$1.$2>
   

5. lastly, the MAIL500 definition which specifies the location of the executable

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

Some of the benefits and caveats:

• virtually unlimited
  • ``local'' users/mailboxes
  • ``local'' mailing lists
• no need to constantly change Sendmail or Sendmail ``databases'' as users/lists change
• easy to add/change simple Sendmail rules to expand groups of mailboxes handed off to LDAP/MAIL500
• needs reliable/backup LDAP server(s)
• LDAP server scalability could be an issue for large volumes of mail handling