SMTP and POP3: Communicating with email Servers

  s an ૰ u H

  2 ©

  2 SMTP and POP3:

Communicating with email Servers

  Defiani Ar둰anildy,둰 M.Si 0818 0296 4763 deff_i둰anildy,yy,i૰oo.cooy Overview

• s

  Se둰vicoe vii Eyiil

  an ૰

• u

  Seandiang Eyiil

  H

  2

• SMTP

  2 ©

• POP3
• Coancolusioan

  Services via Email

• Eyiil is ian Iante둰anet ipplicoitioan t૰it is

  ns uh H iviilible widely,: it coian be icocoessed

  2

  00

  2 f둰oy liptops둰 desktops둰 PDArs둰 yobile

  © p૰oanes둰 iand pige둰s

• Iyigiane ian ipplicoitioan t૰it coian 둰ecoeive eyiil f둰oy i use둰둰 pe둰fo둰y t૰e se둰vicoes 둰equested by, o둰 oan be૰ilf of t૰e use둰둰 iand t૰ean seand t૰e 둰esults bicok to t૰e use둰 vii eyiil

Sending an email

• s

  Eve둰y, eyiil yust ૰ive i destianitioan eyiil

  an ૰ u

  idd둰ess. Aran eyiil idd둰ess tikes t૰e followiang

  H

  2

  fo둰y:

  2 ©

• T૰e doyiian aniye ian ian eyiil idd둰ess geane둰illy, does anot iancolude t૰e “www” p둰efx둰 w૰ico૰ is cooyyoan fo둰 Web site idd둰esses
• Eyiils i둰e anot iyyediitely, delive둰ed to t૰e 둰ecoipieant; iansteid둰 t૰ey, i둰e ianitiilly, seant to y,ou둰 ISP’s o둰 cooypiany,’s yiil se둰ve둰.

  2

  ©

  2 H u ૰ an s

• Eyiils i둰e seant usiang t૰e siyple yiil t둰iansfe둰 p둰otocool (SMTP)
• Ian o둰de둰 to dete둰yiane t૰e 둰ecoipieant’s yiil se둰ve둰둰 i DNS yiil exco૰iange (MX) que둰y, is issued to t૰e locoil DNS se둰ve둰 fo둰 t૰it doyiian aniye

Electronic Mail

• Three major components:

   user agents

   mail servers

   simple mail transfer protocol: SMTP

  User Agent  a.k.a. “mail reader”

   composing, editing, reading mail messages

   e.g., Eudora, Outlook, elm, Mozilla Thunderbird

   outgoing, incoming messages user mailbox outgoing message queue mail server user agent user agent user agent mail server user agent user mail server user agent

  ©

  2

  2 H u ૰ an s

SMTP SMTP SMTP

  Electronic Mail: mail servers

• Mail Servers

   mailbox contains incoming messages for user

   message queue of outgoing (to be sent) mail messages

   SMTP protocol between mail servers to send email messages

   client: sending mail server

   “server”: receiving mail server mail server user agent user agent user agent mail server user agent mail server user agent

  ©

  2

  2 H u ૰ an s

SMTP SMTP SMTP

  [RFC 2821] Electronic Mail: SMTP  uses TCP to reliably transfer email message from client to server,

  s an ૰

  port 25

  u H

  2

   direct transfer: sending server to receiving server

  2

   three phases of transfer

  ©

   handshaking (greeting)

   transfer of messages

   closure

   command/response interaction

   commands: ASCII text

   response: status code and phrase

   messages must be in 7-bit ASCII Scenario: Alice sends message to Bob

• •

  4) SMTP client sends Alice’s
• 1) Alice uses UA to compose message over the TCP message and “to”

  s an

  connection

  ૰

  bob@someschool.edu

  u

• •

  H

  5) Bob’s mail server places

• 2

  2) Alice’s UA sends the message in Bob’s

  2

  message to her mail server;

  ©

  mailbox message placed in message

• •

  6) Bob invokes his user queue

  agent to read message

• 3) Client side of SMTP opens TCP connection with Bob’s mail server

  1 mail mail user server user server agent

  2 agent

  6

  3

  4

  5 SMTP Simple Mail Transfer Protocol

• Ar seande둰-SMTP estiblis૰es i two-wiy, t둰iansyissioan co૰iananel to i 둰ecoeive둰- SMTP oan PORT 25
• HELO cooyyiand “HELO eang둰.sco.edu”
• MArIL

  cooyyiand “MArIL <SP> FROM: idd둰ess<CRLF>”

  ©

  2

  00

  2 H uh ns

• RCPT cooyyiand “RCPT <SP> TO: idd둰ess<CRLF>”
• DArTAr cooyyiand
• Eand-of-yiil iandicoito둰
• QUIT

Architectural View of SMTP ns

  Sender – SMTP uh H

USER

  2 mailbox.engr.sc.edu

  00

  1 2 ©

  SMTP Commands/Replies PORT 25 Receiver – SMTP

  USER Sample SMTP interaction S: 220 hamburger.edu

C: HELO crepes.fr

  s an ૰

S: 250 Hello crepes.fr, pleased to meet you

  u H

C: MAIL FROM: <alice@crepes.fr>

  2 S: 250 alice@crepes.fr... Sender ok

  2 ©

   C: RCPT TO: &lt;bob@hamburger.edu&gt; S: 250 bob@hamburger.edu ... Recipient ok

   C: DATA S: 354 Enter mail, end with "." on a line by itself

   C: Do you like ketchup?

   C: How about pickles? C: . S: 250 Message accepted for delivery

   C: QUIT S: 221 hamburger.edu closing connection

  Mail message format

• SMTP: protocol for exchanging

  s an ૰

  email msgs

  u

  header

  H

• 2

  blank RFC 822: standard for text message format:

  2

  line

  ©

   header lines, e.g.,

   To: body

   From:

   Subject: different from SMTP commands!  body

   the “message”, ASCII characters only

  

Message format: multimedia extensions



  MIME: yultiyedii yiil exteansioan둰 RFC 2045둰 2056  idditioanil lianes ian ysg ૰eide둰 decoli둰e MIME cooanteant ty,pe

   Ty,pes: Uueancoode둰 bise64둰 Quoted-p둰iantible

  multimedia data type, subtype, parameter declaration method used to encode data MIME version encoded data

  ©

  2

  2 H u ૰ an s

From: alice@crepes.fr To: bob@hamburger.edu Subject: Picture of yummy crepe. MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Type: image/jpeg base64 encoded data ..... ......................... ......base64 encoded data

MIME

  s an ૰ u H

  2

  2 © Mail access protocols SMTP SMTP access

  s

  user

  an

  user

  ૰

  protocol

  u

  agent agent

  H

  2

  2

  receiver’s mail sender’s mail

  ©

  server server 

  SMTP: delivery/storage to receiver’s server 

  Mail access protocol: retrieval from server 

  POP: Post Office Protocol [RFC 1939]

• authorization (agent &lt;--&gt;server) and download

  

  IMAP: Internet Mail Access Protocol [RFC 1730]

• more features (more complex)
• manipulation of stored msgs on server

   Try SMTP interaction for yourself:

• s

  telnet servername 25

  an ૰ u

• H

  see 220 둰eply, f둰oy se둰ve둰

  2

• 2

  eante둰 HELO둰 MArIL FROM둰 RCPT TO둰 DArTAr둰 QUIT

  ©

  cooyyiands ibove lets y,ou seand eyiil wit૰out usiang eyiil colieant (둰eide둰)

  21- SMTP: fnal words SMTP uses pe둰sisteant

• s

  Coypi둰isoan wit૰

  an ૰ u

  cooananecotioans HTTP:

  H

  2 SMTP 둰equi둰es yessige

• HTTP: pull
• 2

  (૰eide둰 &amp; body,) to be ian

  ©

• 7-bit ArSCII SMTP se둰ve둰 uses

  SMTP: pus૰

  bot૰ ૰ive ArSCII CRLF.CRLF to dete둰yiane cooyyiand/둰espoanse eand of yessige iante둰icotioan둰 stitus coodes HTTP: eico૰ objecot

• eancoipsulited ian its owan 둰espoanse ysg SMTP: yultiple objecots
• 21-

POP3 Post-Ofice Protocol

• ns

  POP3 is used to 둰ecoeive eyiil yessiges vii i uh H

  00

  2 TCP/IP cooananecotioan; i colieant estiblis૰es i

  2 cooananecotioan wit૰ i POP3 se둰ve둰 it PORT 110

  © Arut૰o둰izitioan stite

• USER ૰u૰ans PArSS ***** T둰iansicotioan stite
• STArT
• OK &lt;SP&gt; # of yessiges &lt;SP&gt; size of yiilbox
• RETR 45

  Respoanse: Heide둰 &lt;CRLF&gt; Messige cooanteant

  Ret둰ieve cooyyiand POP3 protocol S: +OK POP3 server ready

C: user bob S: +OK

• iut૰o둰izitioan p૰ise

  s

C: pass hungry

  an ૰

   colieant cooyyiands: S: +OK user successfully logged on

  u H

  

  2

  user: decoli둰e use둰aniye

C: list

  

  2

  pass: pisswo둰d

S: 1 498

  ©

S: 2 912

   se둰ve둰 둰espoanses S: .

  

• +OK

C: retr 1

  

• -ERR

S: <message 1 contents> S:

  colieant: t둰iansicotioan p૰ise둰

C: dele 1

   list: list yessige anuybe둰s

C: retr 2

  

S: <message 1 contents>

  retr: 둰et둰ieve yessige by, S: . anuybe둰

C: dele 2

   dele: delete

C: quit

   quit

  POP3 server signing off POP3 (more) and IMAP

• More about POP3
• IMAP

  s

  

  an

  Previous example uses  Keep all messages in one

  ૰ u

  “download and delete”

  H

  place: the server

  2 mode.

   Allows user to organize

  2 ©

   Bob cannot re-read e-mail if messages in folders he changes client

  

  IMAP keeps user state 

  “Download-and-keep”: across sessions: copies of messages on

   names of folders and different clients mappings between

   POP3 is stateless across message IDs and folder sessions name

  Example POP3 Interaction /*********** Arfte둰 Coananecotioan ************/

• OK Mico둰osoft Exco૰iange POP3 se둰ve둰 ve둰sioan 5.5.2654.50 둰eidy, /* SERVER */

  ns  USER s૰둰off

  /* CLIENT */ uh

• OK

  

/* SERVER */

H

  2  PArSS **********

  /* CLIENT */

  00

  2 ©

• OK Use둰 sucocoessfully, logged oan /* SERVER */  STArT

  

/* CLIENT */

• OK 107 1545500 /* SERVER */  RETR 107 /* CLIENT */
• OK

  

/* SERVER */ /* HEArDER둰 BLArNK LINE둰 CONTENT */ Recoeived: f둰oy iyo-y03.yx.iol.cooy ([64.12.136.6]) by, yiilbox.eang둰.sco.edu wit૰ SMTP F둰oy: Hy412000yiol.cooy Dite: Tue둰 18 Sep 2001 00:06:54 EDT Subjecot: Re: CSCE826 Hoyewo둰k To: HUHNSyeang둰.sco.edu Example SMTP Interaction

/*********** Arfte둰 Coananecotioan ************/

220 t૰eusco.cosd.sco.edu ESMTP Seandyiil 8.9.0/8.9.0; Moan둰 24 Sep 2001 00:58:05 –

  0400 /* SERVER */ ns

  HELO eang둰.sco.edu /* CLIENT */ uh H

  

250 t૰eusco.cosd.sco.edu Hello l-1d11-14.eangianee둰iang [129.252.26.88] pleised to yeet

  2

  00 y,ou /* SERVER */

  2 © MArIL FROM: step૰eansyeang둰.sco.edu /* CLIENT */ 250 step૰eansyeang둰.sco.edu... Seande둰 ok /* SERVER */ RCPT TO: ૰u૰ansyeang둰.sco.edu /* CLIENT */ 250 step૰eansyeang둰.sco.edu... Recoipieant ok /* SERVER */ Diti /* CLIENT */ 354 Eante둰 yiil둰 eand wit૰ "." oan i liane by, itself /* SERVER */ Dite: Moan Sep 24 01:00:53 EDT 2001 /* CLIENT */ F둰oy: step૰eansyeang둰.sco.edu Subjecot: 둰esult fo둰 y,ou둰 que둰y, iany, old yessige . /* PERIOD Siganiliang Eand-of-Messige */

POP3 and SMTP

  s an ૰ u H

  2

  2 ©

Service Example: Data and Document Access

  ©

  2

  00

  2 H uh ns

  1DB

  2Txt File

USER Application

  3Word Doc

  4ExcelSheet

  5HTML

  6Image

  7Directory Database SpreadSheet

  Files Directory Application receives and sends email Data and Document Access (cont.)

• T૰e se둰vicoe ipplicoitioan 둰ecoeives yessiges seant by, “USER”

  ©

  2

  00

  2 H uh ns

• “USER” specoifes fle ty,pe ian SUBJECT feld
• E.g.둰 DIR둰 HTML둰 DB둰 ArLL (fo둰 fle listiang)둰 etco.
• “USER” specoifes aniye of fle둰 que둰y,둰 o둰 cooyyiand ian CONTENT feld
• Arpplicoitioan 둰etu둰ans 둰esults eit૰e둰 is eyiil cooanteant o둰 ittico૰yeant

Conclusion

• s SMTP is used to seand eyiils f둰oy colieant to se둰ve둰.

  an ૰

• u

  POP3 is used to 둰ecoeive eyiils f둰oy se둰ve둰 to

  H

  2 colieant.

  2

• ©

  POP3 coian be used to delete eyiils f둰oy t૰e se둰ve둰 oancoe 둰ecoeived.