8.4 Mail Agenten MDA MSA MUA MUA. Vorläufige Version 355 c 2003 Peter Thiemann

Transkript

1 8.4 Mail Agenten MTA MTA MDA MUA MSA MUA Vorläufige Version 355 c 2003 Peter Thiemann

2 MUA Mail User Agent, Benutzerschnittstelle, Erstellen von Mails (mail, pine, mh, outlook express, nsmail,... ) Kommunikation: Programmaufruf, SMTP MTA Mail Transfer Agent, Routing von Mails (sendmail, qmail, postfix,... ) Kommunikation: Programmaufruf, SMTP MDA Mail Delivery Agent, Zustellung der Mail in die Mailbox (mail, deliver, qmail, procmail,... ) Kommunikation: Programmaufruf, IMAP, Dateizugriff MSA Mail Storage Agent, Mailspeicher (imap) Kommunikation: IMAP, POP, Dateizugriff MUA Mail User Agent, Lesen von Mails Vorläufige Version 356 c 2003 Peter Thiemann

3 8.5 Simple Mail Transfer Protocol (SMTP) RFC 2821 (Revision) Stream Protokoll, port 25 smtp Mail Transport, Delivery, Submission MTA SMTP client SMTP MTA SMTP server MDA (SMTP) MUA MSA MUA Vorläufige Version 357 c 2003 Peter Thiemann

4 SMTP Client sendmessage client server sender recipients message = withsocketsdo $ do h <- connectto (name server) (Service "smtp") hsetbuffering h LineBuffering result <- runsmtp $ do hrun h GREETING -- parse server s greeting hrun h (HELO (cname client)) -- introduce yourself hrun h (MAIL sender []) -- envelope: specify sender let g r = hrun h (RCPT r []) -- envelope: one recipient mapm_ g recipients hrun h DATA -- indicate start of data hrun h (LINES message) -- transmit message quitresult <- runsmtp $ hrun h QUIT -- finish the conversation hclose h Vorläufige Version 358 c 2003 Peter Thiemann

5 Belauschte Konversation > telnet localhost smtp 220 kailua.informatik.uni-freiburg.de ESMTP Sendmail /8.12.2/SuSE Linux 0.6; Tue HELO kailua 250 kailua.informatik.uni-freiburg.de Hello localhost [ ], pleased to meet you MAIL FROM: thiemann thiemann... Sender ok RCPT TO: Recipient ok DATA 354 Enter mail, end with "." on a line by itself Hallo nur ein Test h61loilx Message accepted for delivery QUIT kailua.informatik.uni-freiburg.de closing connection Connection closed by foreign host. Vorläufige Version 359 c 2003 Peter Thiemann

6 Erweiterungen Ursprünglich: 7bit Transportprotokoll ESMTP definiert Rahmen für Erweiterungen Beispiel: 220 kailua.informatik.uni-freiburg.de ESMTP Sendmail /8.12.2/SuSE Linux 0.6; Tue EHLO localhost 250-kailua.informatik.uni-freiburg.de Hello localhost [ ], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 250-DSN 250-ETRN 250-AUTH GSSAPI 250-DELIVERBY 250 HELP Vorläufige Version 360 c 2003 Peter Thiemann

7 Spezifikation der Erweiterungen Parameter der verschickten Mail (Größe, 8bit?, Zeitraum) MAIL FROM: reverse-path [SP mail-parameters ] CRLF Empfängerparameter RCPT TO: forward-path [SP rcpt-parameters ] CRLF Vorläufige Version 361 c 2003 Peter Thiemann

8 8.6 Post Office Protocol (POP3) RFC 1939 Mail Abholung für PC-artige Computer nicht ständig eingeschaltet nicht genug Ressourcen für MTS (message transfer system) d.h. MTA und MDA Zustellung auf zentralem Server geringer Funktionsumfang Stream Protokoll, Port 110 pop3 Vorläufige Version 362 c 2003 Peter Thiemann

9 Übersicht POP3 S: Greeting AUTHORIZATION STATE QUIT USER username PASS password TRANSACTION STATE STAT LIST RETR DELE NOOP RSET APOP name digest QUIT UPDATE STATE <<server expunges deletions>> Vorläufige Version 363 c 2003 Peter Thiemann

10 Authentisierung USER name, PASS word überträgt Information im Klartext APOP name digest berechnet digest aus Nonce (in der Begrüßung) und Geheimnis (Passwort) (nur möglich, falls Nonce vorhanden) S: +OK POP3 server ready C: APOP mrose c4c9334bac560ecc979e58001b3e22fb S: +OK maildrop has 1 message (369 octets) Nonce: < @dbc.mtview.ca.us> Geheimnis: tanstaaf Digest=MD5(Nonce+Geheimnis) =MD5(< @dbc.mtview.ca.us>tanstaaf) =c4c9334bac560ecc979e58001b3e22fb Vorläufige Version 364 c 2003 Peter Thiemann

11 Diskussion Vorteile: einfach und klein, Grundfunktionalität Nachteile: Mailgefängnis PC Zusammenarbeit? Datensicherheit? keine Suche und Bearbeitung keine Offline Verarbeitung Vorläufige Version 365 c 2003 Peter Thiemann

12 8.7 Internet Message Access Protocol (IMAP4) RFC 1730 Zweck:... access and manipulate electronic mail messages on a [centralized] server. manipulation of remote message folders operations for creating, deleting, and renaming mailboxes; checking for new messages; permanently removing messages; setting and clearing flags; RFC 822 and MIME parsing; searching; and selective fetching of message attributes, texts, and portions thereof. Vorläufige Version 366 c 2003 Peter Thiemann

13 Übersicht IMAP4 initial connection and server greeting non authenticated authenticated selected logout and close connection Vorläufige Version 367 c 2003 Peter Thiemann

14 Authentisierung Typischer Ablauf LOGIN Name Passwort (Klartext OK, falls über SSL/TLS oder direkte Einwahl) AUTHENTICATE... (authenticated) Kommandos auf Mailboxen: Erzeugung, Umbenennung, Aktivieren,... Auswahl einer Mailbox... (selected) Kommandos auf Messages: Suche, Zugriff, Abspeichern, Kopieren Vorläufige Version 368 c 2003 Peter Thiemann

15 Zugriff auf Nachrichten sequentielle Numerierung innerhalb einer Mailbox kurzlebig, da ständige Änderung UID/UIDVALUE (je 32 Bit) Mailbox identifiziert durch Name und UIDVALUE UID = eindeutiger Bezeichner einer Nachricht in einer Mailbox Vergabe der UIDs erfolgt aufsteigend, aber nicht notwendig zusammenhängend Änderung des Mailboxnamens UIDs werden ungültig UID/UIDVALUE verwendet für Synchronisation zwischen Client und Server Probleme Eindeutigkeit nur innerhalb einer Mailbox / eines UIDVALUE Mehrere Server nicht vorgesehen Vorläufige Version 369 c 2003 Peter Thiemann

16 Beispielsitzung S: * OK IMAP4 Service Ready C: a001 login mrc secret S: a001 OK LOGIN completed C: a002 select inbox S: * 18 EXISTS S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * 2 RECENT S: * OK [UNSEEN 17] Message 17 is the first unseen message S: * OK [UIDVALIDITY ] UIDs valid S: a002 OK [READ-WRITE] SELECT completed C: a003 fetch 12 full S: * 12 FETCH (FLAGS (\Seen) INTERNALDATE "14-Jul :44: " RFC822.SIZE 4282 ENVELOPE ("Wed, 14 Jul :23: (PDT)" "IMAP4 WG mtg summary and minutes" (("Terry Gray" NIL "gray" "cac.washington.edu")) (("Terry Gray" NIL "gray" "cac.washington.edu")) (("Terry Gray" NIL "gray" "cac.washington.edu")) ((NIL NIL "imap" "cac.washington.edu")) ((NIL NIL "minutes" "CNRI.Reston.VA.US") ("John Klensin" NIL "KLENSIN" "INFOODS.MIT.EDU")) NIL NIL "<B @cac.washington.edu>") BODY ("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" )) S: a003 OK FETCH completed Vorläufige Version 370 c 2003 Peter Thiemann

17 C: a004 fetch 12 rfc822.header S: * 12 FETCH (RFC822.HEADER {346} S: Date: Wed, 14 Jul :23: (PDT) S: From: Terry Gray <gray@cac.washington.edu> S: Subject: IMAP4 WG mtg summary and minutes S: To: imap@cac.washington.edu S: cc: minutes@cnri.reston.va.us, John Klensin <KLENSIN@INFOODS.MIT.EDU> S: Message-Id: <B @cac.washington.edu> S: MIME-Version: 1.0 S: Content-Type: TEXT/PLAIN; CHARSET=US-ASCII S: S: ) S: a004 OK FETCH completed C: a005 store 12 +flags \deleted S: * 12 FETCH (FLAGS (\Seen \Deleted)) S: a005 OK +FLAGS completed C: a006 logout S: * BYE IMAP4 server terminating connection S: a006 OK LOGOUT completed Vorläufige Version 371 c 2003 Peter Thiemann

18 8.8 RMS: A Robust Mail Store and Retrieval System Scenario 1: Net Nomads Users of multiple computing devices at multiple locations with unreliable connectivity Consequence: parts of the nomad s workspace are replicated over these machines Vorläufige Version 372 c 2003 Peter Thiemann

19 The nomad s problem File Synchronization Vorläufige Version 373 c 2003 Peter Thiemann

20 The Nomad s Nightmare Replicated Mailbox Synchronization Vorläufige Version 374 c 2003 Peter Thiemann

21 An Example origin mailbox with folders inbox, work, and inbox.october setting replicas A and B of that mailbox actions 1. Reorganize A: move messages 5, 13, 19 from inbox to work. 2. Reorganize B: move messages 1-10 from inbox to inbox.october. 3. Incorporate A: Adds message X to inbox. 4. Incorporate B: Adds message Y to inbox. Vorläufige Version 375 c 2003 Peter Thiemann

22 Scenario 2: Networked Collaboration Multiple users work with the same set of mailboxes independent reorganization multiple servers disconnected operation Vorläufige Version 376 c 2003 Peter Thiemann

23 Design Goals of RMS support for replication: all operations work in disconnected mode on replicas; automatic merging of replicas; access to messages based on attributes, not on accidental hierarchical structure; multi-user collaborative operation. Vorläufige Version 377 c 2003 Peter Thiemann

24 Principles separation of message data and meta data message data is immutable meta data (including organizational attributes) changes over time all data pertaining to a message is stored via a content-based unique identifier constructed from a cryptographic hash of the message s contents example: urn:cbuid:message/rfc822;mode=1:md5:*/d97a43ed c363b00bd27411fa7 Intention part 1: cbuid replaces IMAP s UID Vorläufige Version 378 c 2003 Peter Thiemann

25 Operations Overview MDA:deliver MSA:deliver Mail Drop MSA:inc mail store MSA:select user1 user2 collections MSA:retrieve any user Vorläufige Version 379 c 2003 Peter Thiemann

26 Mail Store as an Abstract Datatype data RMS a data Message data MC data MailStore -- mail store monad (abstract) -- an message -- a message collection (abstract) -- external representation of a mail store setuser :: UserName -> RMS Bool -- root only incorporate :: Message -> [Attr] -> RMS () select :: Select -> RMS MC retrieve :: (MC, Int) -> RMS Message replace :: [Attr] -> [Attr] -> MC -> RMS () remove :: MC -> RMS () replicate :: MC -> RMS MailStore integrate :: MailStore -> RMS () Vorläufige Version 380 c 2003 Peter Thiemann

27 Query Data Structure data Select = Collection { mcname :: String, mcselect :: Maybe [Int] } EarlierThan { seldate :: String } LaterThan { seldate :: String } Not Select And [Select] Or [Select] Attributes [String] Header { hdname :: String, hdcont :: String } Vorläufige Version 381 c 2003 Peter Thiemann

28 Internal Structure data CBUID -- content-based unique identifier -- abstract data MC = MC RandomNumber data RMSState = RMSState { data :: CBUID -> Maybe Message, meta :: UserName -> CBUID -> Maybe [Attr], coll :: MC -> Maybe [CBUID] } Vorläufige Version 382 c 2003 Peter Thiemann

29 Implementation of Internal Structure $MAILSTORE/ data/ meta/ coll/ GUMD1 GUMD2... USER1/ USER2/... MC1 MC2... GUMD1 GUMD Vorläufige Version 383 c 2003 Peter Thiemann

30 More Implementation Stuff incorporate implemented in C using Bernstein s mess822 library and Peter Deutsch s implementation of MD5. shell scripts for mailbox conversion using formail incorporate, select, retrieve, replace, remove, replicate, integrate implemented in Haskell server-based implementation with caching WWW-based mail access utility implemented with WASH Vorläufige Version 384 c 2003 Peter Thiemann

31 Conclusion design goals met (replication, synchronization, attribute-based access, multi-user) additional benefits message collections may be communicated to external users to grant them (Web-based) access to the mail store. Forwarding of messages can be reduced to passing an MC. CBUID reliably detects duplicate messages within store. Vorläufige Version 385 c 2003 Peter Thiemann