Using Exim with LDAP

1. Using Exim with LDAP Douglas Gray Stephens Senior Directory ArchitectSchlumberger

2. Topics • What is LDAP; • What is LDAP designed for; • How is LDAP integrated into Exim; • Case study of using Exim with LDAP; • How to trouble shoot Exim with LDAP;

3. What is LDAP • Light weight Directory Access Protocol; • (X.500 is DAP, so more heavy weight); • Communications protocol : • no specification for back end server system; • Standards based; • Defacto standard for internet white pages (c.f. http for on line documents). • Current version is LDAPv3 (ratified in 2000)

4. What is LDAP designed for • Systems where there are few writes, but many reads; • Storing any data; • Fast response for queries; • Redundancy (i.e automatic fail over);

5. What is LDAP not designed for • It is not a relational database; • Is not efficient for systems with frequent writes; • Server may return unexpected (e.g. no) results if attribute not indexed.

6. How is data stored in LDAP (DIT) • LDAP is a tree structure (Document Information Tree):

7. LDAP searches • Require • Server to search (where to look); • Search root (part of DIT to start searching from); • Scope (how far to look ─ base, one level, or sub tree); • Filter (what to look for); • Attribute(s) to return;

8. LDAP search example • E.g. ldapsearch –h myhost:389 –b dc=company1,dc=com –s sub “(cn=douglas gray stephens)” cn sn givenname mail • Returnsdn: cn=Douglas Gray Stephens,ou=employee,dc=company1,dc=com cn: Douglas Gray Stephens cn: Douglas Gray-Stephens cn: Grey Stevens sn: Gray Stephens givenName: Douglas mail: dgs1@skibass.org

9. LDAP filters • Components of filter nested within brackets “(…..)”; • Items can be ANDed together (with “&”); • Items can be ORed together (with “|”); • Items can be negated (with “!”); • Searches can include wild cards (with “*”); • RFC 2254 gives full details.

10. LDAP filter example • E.g. “(&(mail=*)(c=gb)(!(l=london))(cn=douglas*))” • Means • Find all records with an mail attribute • that are in the United Kingdom (GB) • and are do not have London as the city • and have a common name starting with douglas

11. LDAP URLs • An LDAP URL begins with the protocol prefix "ldap" and is defined by the following grammar, as defined in RFC 2255: <ldapurl> ::= "ldap://" [ <host:port> ] "/" <dn> [ "?" <attributes> [ "?" <scope> "?" <filter> ] ] <host:port> ::= <hostname> [ ":" <portnumber> ] <dn> ::= a string as defined in RFC 2253 <attributes> ::= NULL | <attributelist> <attributelist> ::= <attributetype> | <attributetype> [ "," <attributelist> ] <attributetype> ::= a string as defined in RFC 1777 <scope> ::= "base" | "one" | "sub" <filter> ::= a string as defined in RFC 2254

12. LDAP URL example • ldap://server1 server2:387/dc=com?cn,mail?sub?(&(cn=douglas*)(l=cambridge)) • Specifies that • there are two servers to try (server1, then server2). Note the second server is on a non standard port (387); • a search root of “dc=com”; • attributes “cn” and “mail” should be returned; • the sub tree should be searched; • using a filter “(&(cn=douglas*)(l=cambridge))”;

13. Building Exim • Requires that the LDAP libraries be available • OpenLDAP (http://www.openldap.org/); • SunOne (previously Netscape/iPlanet) (http://www.sun.com/software/products/directory_srvr_ee/ ) • Specify in Makefile LOOKUP_LDAP=yes LDAP_LIB_TYPE=OPENLDAP1/OPENLDAP2/NETSCAPE/SOLARIS LOOKUP_INCLUDE=-I /???/include LOOKUP_LIBS=-L/???/lib -lldap -llber

14. Configuring Exim • Location of LDAP servers ldap_default_servers = “\ localhost::389 : \ server1::389 : \ server2::387” • Some router/transport commands to make use of LDAP (use anywhere that you would use the exim lookup functionality).

15. LDAP lookups in Exim • Types of lookups: • ldaprequires the result to contain just one entry; if there are more, it gives an error. • ldapdnalso requires the result to contain just one entry, but it is the Distinguished Name that is returned rather than any attribute values. • ldapmpermits the result to contain more than one entry; the attributes from all of them are returned;each entry in result string is on a separate line;

16. LDAP lookup results • ldap:///o=base?attr1?sub?(uid=frederic) value1.1, value1.2 • ldap:///o=base?attr2?sub?(uid=frederic) value two • ldap:///o=base?attr1,attr2?sub?(uid=frederic) attr1="value1.1, value1.2" attr2="value two" • ldap:///o=base?objectclass,cn,sn?sub?(uid=frederic) objectClass="top, person" cn=“Frederic Smith, Fred Smith" sn=“Smith“ • ldapm:///o=base??sub?(uid=fred*) objectClass="top,person" attr1="value1.1, value1.2" attr2="value two“ objectClass="top,person" …. Etc. for the second match

17. Case study • Objective • Look up names in LDAP and forward to appropriate person; • Handle instance when multiple matches; • Handle instance when there is no email address; • Enable user to control lookup options (so limiting spam).

18. Details of mail handling • Addresses of the form uid@company.com will always be sent to only one person, since a uid is by definition unique within the directory.; • Addresses of the form abc.efg_hij-mno@company.com will be processed according to the following rules. • Forward to record that matches uid and has email address • Forward to record that matches the common name(s) • Forward to record that givename/surname • Forward to a record that contains all the words in the common name(s) • If record does not have email address, return phone number • If there are 2 to 5 matches, give more details to sender • If there are more than 5 matches, bounce message

19. Mail processing • For a single match, the message is forwarded to that address; • For 2 to 5 matches, the message is bounced back to the sender along with details of the matches. The sender is asked to try again. • For more than 5 matches, the message is bounced back to the sender. The sender is asked to be more specific about the address.

20. Message flow Loop through series of LDAP lookups Zero or more than one matches is failure for ldapm lookup • Perl code alias_bounce handles • no matches • 2 to 5 matches • more than 5 matches • No email address (snail mail details) Perl code ldap_one sets new_address and status

21. Perl function that builds up an LDAP filter Exim Global parameters • ldap_default_servers = “server1 server2:387” • What should be returned: LDAP_URL = ldap:///dc=comany1,dc=com?uid,mail,cn,ou,telephonenumber,o?sub? • Search definitions for different lookups: • MAIL_UID_MATCH = &(mail=*)(uid=${perl{punc_to_dash}{$local_part • MAIL_CN_MATCH = &(mail=*)(cn=${perl{punc_to_spc}{$local_part}}) • MAIL_GIVENNAME_SN_MATCH = &(mail=*)(${perl{givenname_sn_match}{$local_part}}) • MAIL_CN_WORDS_MATCH = &(mail=*)(${perl{cn_match}{$local_part}})

22. Returns mail address when one match LDAP router example company1_user: driver = redirect allow_defer allow_fail condition = "${perl{ldap_who} \ {${lookup ldapm {LDAP_URL(MAIL_UID_MATCH)}{$value} \ {${lookup ldapm {LDAP_URL(MAIL_CN_MATCH)} {$value} \ {${lookup ldapm {LDAP_URL(MAIL_GIVENNAME_SN_MATCH)} {$value} \ {${lookup ldapm {LDAP_URL(MAIL_CN_WORDS_MATCH)} {$value} \ {DUNNO}}}}}}}}}}" data = ${perl{new_address}} domains = company1.com headers_add = "X-LDAP-Alias: V LDAP_ALIAS_VERSION. Sent to $local_part@$domain resolving to ${perl{new_address}}" retry_use_local_part

23. Bounce router unknownuser: driver = accept retry_use_local_part transport = uid_bounce no_verify

24. Bounce transport uid_bounce: driver = autoreply from = Comapny1 Mail Server <mailer-daemon@org.com> headers = "X-LDAP-To: bouncing ${local_part}@${domain} (${perl{failure_reason}})\n\ Mime-Version: 1.0\nContent-Type: multipart/mixed; boundary=\"${perl{mime_boundary}}\"" log = "/var/spool/exim/log/bouncelog" once = "/var/spool/exim/db/bounce/${local_part}" once_repeat = 1w return_message subject = "Unable to deliver to ${local_part}@${domain}" text = ${perl{mime_bounce}{${domain}}} to = $sender_address transport_filter = "/etc/exim/close_mime ${perl{mime_boundary}}"

25. Sample too many matches From: Company1 Mail Server <mailer-daemon@slb.com> Subject: Unable to deliver to few@company1.com …… To help you locate the correct individual, selected fields from the possible matches are included below. The uid field is the only onemguaranteed unique within a given community. Name : Andy Few Uid : AFew1 Email : aFew1@london.company1.com Organisation : Company1 City : london Name : Alex Few Uid : afew2 Email : afew2@cambridge.company1.com Organisation : Company1 City : cambridge

26. Example with no email address From: Company1 Mail Server <mailer-daemon@slb.com> Subject: Unable to deliver to dages1@company1.com Dear email sender, This message has been automatically generated because I, the email server, found a single match looking for <dages1@company1.com> but that match contained no forwarding email address and was thus undeliverable. The details of this match are as follows: Name : Dark Ages Uid : dages1 Organisation : Company1 City : Oxford Tel : +44 1865 1234567

27. Trouble shooting • Test out address resolution • exim -bt dgraystephens@company1.com dgs1@skibass.org <-- dgraystephens@company1.com router = perimeter_routes, transport = remote_smtp host mail-relay.slb.com [163.184.1.20] host mail-relay.slb.com [134.32.26.55] host mail-relay.slb.com [163.187.152.23] host mail-relay.slb.com [163.188.150.130]

28. Trouble shooting (cont) • Additional debugging exim -d+lookup -bt dgraystephens@company1.comShows details including LDAP callsdatabase lookup required for …….. perform_ldap_search: ldapm URL = "ldap:///dc=company1,dc=com?uid,mail,cn,ou,telephonenumber,o?sub?(&(mail=*)(uid=dgraystephens))" server=localhost port=389 sizelimit=0 timelimit=0 tcplimit=-1 after ldap_url_parse: host=localhost port=389 ldap_initialize with URL ldap://localhost:389/ …… ldap_parse_result yielded 0: Success LDAP search: returning: cn="Douglas Gray Stephens, Douglas Gray-Stephens, Grey Stevens" mail="dgs1@skibass.org" o="Company1" ou="Core services" uid="dgraystephens" telephoneNumber="44 1223 325295 “ Check LDAP server logs for connection details

29. Controlling fuzzy logic or spam • Fuzzy logic is good when there is no spam • If spam is an issue, then enable users to opt in or out • Add new component to searches, e.g.MAIL_CN_MATCH = &(mail=*)(cn=${perl{punc_to_spc}{$local_part}})becomesMAIL_CN_MATCH = &(mail=*)(cn=${perl{punc_to_spc}{$local_part}})(!(description=exclude:cn))