Khi Nim C Bn v in Th (E-Mail)

Phng Thnh Nguyn (rev. 08/12/95)

I - Li m u

in th tc l Electronic Mail cn ܮc gi tt l E-Mail l cch gi in th rt ph bin trong thp nin 80 v 90. E-Mail c nhiu cu trc khc nhau ty thuc vo h thng my vi tnh ca ngܩi s dng. Th d nh h thng truyn tin bng E-Mail VM/CMS ca IBM khc vi h thng truyn tin VMS ca Digital hoc l ca UNIX. Nhng mc d khc nhau v cch cu trc nhng tt c NJu c mt mc ch chung l chuyn gi hoc thu nhn nhng th t in t t mt ni ny qua mt ni khc mt cch tht nhanh chng t vi giy cho ti vi pht hoc vi ting ng h.

Ngy nay nh s bnh trܧng mnh m ca Internet (Mng Lܧi Truyn Tin Ton Cu) ngܩi ta c th gi in th ti cc quc gia trn khp th gii. Vi s hu dng nh vy cho nn E-Mail hu nh tr thnh mt nhu cu cn phi c ca ngܩi s dng my vi tnh. Ti cc nܧc tn tin cng nh cc nܧc ang m mang pht trin, cc trܩng i hc, cc c cu thng mi, cc c quan chnh quyn v.v. NJu v ang mc ni h thng my vi tnh ca h vo Internet Nj s chuyn th in t ܮc mau l v d dng hn.

V trn thc t c rt nhiu h thng vi tnh khc nhau v mi h thng li c cu trc chuyn nhn th in t khc nha V s khc bit nh vy cho nn vic chuyn nhn th in t gia hai h thng khc nhau rt l kh khn v bt tin. V th cho nn ngܩi ta ǥt ra mt nghi thc chung cho in th C ngha l cc h thng my vi tnh NJu ng vi nhau v mt nghi thc chung gi l Simple Mail Transfer Protocol vit tt l SMTP (Nghi Thc n Gin Chuyn Vn Th T). Nh vo SMTP ny m s chuyn vn th t in t trn Internet tr thnh d dng nhanh chng cho tt c cc ngܩi s dng my vi tnh mc du cho d h c xi h thng my vi tnh khc nha

II - iu Kin C Bn

Mun gi th in t ngܩi gi cn phi c mt chng mc (account) trn mt my vi tnh no . Mt my vi tnh c th c mt hoc nhiu chng mc. Mi chng mc NJu ܮc mang mt tn khc nhau (user-id). Mi chng mc NJu c mt hp th ring cho chng mc . Thng thܩng th tn ca hp th s ging nh tn ca chng mc. Ngoi ra my vi tnh phi ܮc ni lin trc tip hoc gin tip vi h thng Internet nu mun ܮc gi th cho ton cu. a s cc hc sinh trong trܩng i hc ܮc cp mt chng mc min ph. Cc nhn vin ca cc c quan chnh ph, cc hng ln nh phn ng NJu ܮc cp chng mc. Cn cc ngܩi s dng my vi tnh ti nh vn c th chuyn vn th in t bng cch mc ni my vi tnh ca h vi mt my vi tnh khc bng my modem (my bin iu/hoa`n iu). C vi ni cp pht chng mc min ph cho cc my vi tnh ti nh c th dng modem Nj mc ni vi my vi tnh Nj chuyn vn th in t. Ngoi ra, cn c rt nhiu c quan thng mi cung cp dch v hoc chng mc cho my vi tnh ti nh nhng ngܩi s dng phi tr tin dch v hng thng. Mt vi c quan thng mi cung cp dch vu./chng mc l Prodigy, CompuServe, American Online v.v.

III - Tin Trnh Chuyn Vn Th

1) Chng Trnh Th (Mail Program)

Mun džc hoc gi nhng th t in t t mt my vi tnh th vi tnh phi c mt Chng Trnh Th (Mail Program). Ci Chng Trnh Th ny s thc hin nhng vic cn thit c bn nh edit (vit th), send (gi), receive (nhn), forward (chuyn tip), reply (tr li), save (lu tr), delete (xa b) v.v. C rt nhiu Chng Trnh Th khc nhau Nj thc hin vic chuyn vn th ty thuc vo H Thng iu Khin (Operating System) trn my vi tnh ca ngܩi s dng. C Chng Trnh Th c sn trn my th d nh mail trn h thng UNIX, mh hoc xmh trn h thng AIX. C nhiu Chng Trnh Th min ph nh ELM, hoc XMailTool v.v. Ngoi ra cn c nhiu loi Chng Trnh Th khc vi nhiu kh nng tin li hn nhng ngܩi s dng phi mua Chng Trnh Th .

2) a Ch Th T (Mail Address)

Tng t nh vic gi th bng bu in, vic gi nhn th in t cng cn phi c a ch ca ni gi v a ch ca ni nhn. a ch ca E-Mail ܮc theo cu trc nh sau:

user-mailbox@domain-part (Hp-thu+@khu-vng)

user-mailbox l a ch ca hp th ngܩi nhn. C th hiu nh s nh, s hm, v tn ܩng nh th bu in. Khu-vng (domain-part) l ni chn ca ngܩi nhn trn Internet. C th hiu n ging nh tn thnh ph, tn tnh v quc gia nh a ch nh trn th bu in.

Th d ca mt dng a ch thng dng nht:

huong@bonghoa.ucdavis.edu

T phi sang tri, "edu" l h thng ca cc trܩng i hc. "ucdavis" l trܩng i Hc Davis ti California. "bonghoa" l tn ca mt my vi tnh trong trܩng Davis. "huong" l tn hp th ca mt chng mc. Trn my vi tnh tn l bonghoa cn c th c nhiu hp th cho nhiu ngܩi khc th d nh lan@bonghoa.ucdavis.edu, dung@bonghoa.ucdavis.edu v.v.

Xin ch l khng hn l mi a ch NJu ghi ch tn ca my ngܩi nhn. Thng thܩng cc c s ln NJu c b tr mt vi my vi tnh ǥc bit Nj chuyn gi v thu nhn in th Th d nh phn ln cc a ch e-mail ca nhn vin IBM NJu mang khu vng ging nhau l VNET.IBM.NET. Tt c cc in th gi v a ch ny NJu qua mt my nhn ti IBM. Sau cn c vo phn hp th (user-mailbox), my ny s chuyn a ch ny (mapping) qua a ch ǥc bit dng trong IBM v l th ny ܮc cc my IBM chuyn ti hp th ngܩi nhn.

Phn cui ca domain-part c th cho ngܩi ta bit phn no v ci a ch u hoc thuc v chnh quyn hay hng xܪng. Th d nh nhng ci ph bin l:

EDU -- Cc trܩng i Hc
GOV -- C quan chnh quyn
MIL -- Qun Ƕi
NET -- nhng trung tm ln cung cp dch v Internet
ORG -- Nhng hi on
CAN -- Canada
AU -- Australia v.v.

a ch th t i khi c dng khc nhng v phm vi ca bi nn khng nu ra ni

3) Tn Hiu (alias)

Mc d a ch gi th ܮc c gng ǥt ra cho mi ngܩi d nh nhng trn thc t c nhiu a ch tht kh nh th d nh l ghf82057@kamsidf.ucdavis.ed Nhng a ch nh vy thܩng rt kh nh v di dng v hay to ra nhng lm ln. V th nhng Chng Trnh Th thܩng cho php ngܩi dng to nhng tn d nh ngn gn. Cch thc to nhng tn hiu nh sau

alias mai ghf82057@kamsidf.ucdavis.edu
alias nam ghi20056@arlin.ucdavis.edu
alias thao kbn3497@vega.ucdavis.edu

Th d nh mun gi ti a ch ghf82057@kamsidf.ucdavis.edu th ngܩi gi ch vic

mail mai

th Chng Trnh Th s t Ƕng sa ǰi tn hiu "mai" thnh a ch ghf82057@kamsidf.ucdavis.edu gim cho ngܩi gi.

Cch thc ny cng c th p dng Nj gi cho mt nhm ngܩi cng mt lc. Th d nh ngܩi gi c th to mt tn hiu mi nh sau

alias banhoc mai nam thao

th khi ngܩi gi mun gi cho ba ngܩi nhn (mai, nam, v thao) cng mt lc th ngܩi gi ch cn nh xung nh sau

mail banhoc

th tt c mi ngܩi trong nhm banhoc s NJu nhn ܮc in th

4) Cch Chuyn Tip in Th (Mail Forwarding)

Trn Internet c rt nhiu nhm hi bao gm rt nhiu ngܩi Nj tho lun hoc bn ci nhiu NJ ti khc nha C nhm ch bao gm vi ngܩi nhng c nhiu nhm quy t ti hng trm hoc hng ngn ngܩi. Vi nhng nhm ng nh vy nu phi nh tn tng a ch th rt cc nhc v kh khn. Mc d c th dng tn hiu Nj gim thiu vic nh my nhng mt nhm c th c thm ngܩi mi hoc c ngܩi rt ra khi nhm thnh ra mi ngܩi phi sa cha ci bi cha Tn Hiu mi khi c s thay ǰi. Nh vy l khng thc t cho nn Chng Trnh Th cho php ngܩi s dng sp xp Cch Chuyn Tip Th Ngܩi s dng c th to ra mt hp th ring bit nu c ai gi th v hp th th Chng Trnh Th s t Ƕng chuyn tip l th cho tt c mi ngܩi nm trong danh sch chuyn tip.

Vi phng cch ny cho php vic gi th ljn mt nhm ng d dng hn. Thay v ngܩi gi phi gi th cho tng ngܩi trong nhm, ngܩi gi ch cn gi mt l th ljn mt hp th chung ti mt my vi tnh no . Ti ni Chng Trnh Th s chuyn th cho tng ngܩi trong danh sch. V ch c mt danh sch chung ti ni chuyn tip cho nn chuyn sa cha thm bt thnh vin ܮc d dng v chnh xc hn nhiu.

5) Cch Chuyn Vn (Mail Delivery)

a) Chuyn Th (Send Mail)

Sau khi ngܩi s dng my vi tnh dng Chng Trnh Th Nj vit th v ghi r a ch ca ngܩi nhn th my in tnh s chuyn bc th in ljn hp th ngܩi nhn. SMTP s dng nghi thc TCP (TCP protocol) Nj chuyn vn th V nghi thc TCP rt l hu hiu v c phn kim sot tht lc mt mt cho nn vic gi th in c hiu xut rt ca Khi nhn ܮc mnh lnh gi i ca ngܩi s dng, my vi tnh s dng nghi thc TCP lin lc vi my vi tnh ca ngܩi nhn Nj chuyn th i khi v my vi tnh ca ngܩi nhn b tt in (power off) hoc ܩng dy mc ni t my gi ti my nhn tm thi b h hng tm thi ti mt ni no (tranmission wire failure), hoc l c th l My Chuyn Tip (routers) trn tuyn ܩng lin lc gia hai my tm thi b h (out of order) th my gi khng cch no lin lc vi my nhn ܮc. Gp trܩng hp nh vy th my gi s tm thi gi l th in trong khu vc d tr tm thi (spool area). My gi sau s tm cch lin lc vi my nhn Nj chuyn th Nhng vic ny xy ra trong my vi tnh v ngܩi s dng s khng hay bit g. y l im khc bit ng ch gia E-Mail v FTP (File Transfer Protocol). Mc d c hai NJu dng nghi thc TCP nhng FTP lc s dng i hi my t xa phi ang hot Ƕng v ܩng lin lc gia hai my phi ܮc thng sut. Ngܮc li E-Mail th khng cn my nhn phi ang hot Ƕng trong lc th ܮc gi, nu gi khng ܮc th Chng Trnh Th s th gi vo khi khc. Nu trong ba ngy m my vi tnh ca ni gi vn khng lin lc ܮc vi my nhn th my gi s gi mt thng bo cho ngܩi gi ni rng vic vn chuyn ca l th in khng thnh cng.

b) Nhn Th (Receive Mail)

Nu my gi c th lin lc ܮc vi my nhn th vic chuyn th s ܮc tin hnh. Trܧc khi nhn l th th my nhn s kim sot tn ngܩi nhn c hp th trn my nhn hay khng. Nu tn ngܩi nhn th c hp th trn my nhn th l th s ܮc nhn ly v l th s ܮc b vo hp th ca ngܩi nhn. Trܩng hp nu my nhn kim sot thy rng tn ngܩi nhn khng c hp th th my nhn s khܧc t vic nhn l th Trong trܩng hp khܧc t ny th my gi s thng bo cho ngܩi gi bit l ngܩi nhn khng c hp th (user unknown).

Sau khi my nhn nhn l th v b vo hp th cho ngܩi nhn th my nhn s thng bo cho ngܩi nhn bit l c th mi . Ngܩi nhn s dng Chng Trnh Th Nj xem l th Sau khi xem th xong th ngܩi nhn c th lu tr (save), hoc xa (delete), hoc tr li (reply) v.v. Trܩng hp nu ngܩi nhn mun tr li li l th cho ngܩi gi th ngܩi nhn khng cn phi ghi li a ch v a ch ca ngܩi gi c sn trong l th v Chng Trnh Th s b a ch vo gim trong bc th tr li.

c) Trm Phc V Th (Mail Server)

Trn thc t, trong nhng c quan v hng xܪng ln, my vi tnh ca ngܩi gi th khng c gi trc tip ti my vi tnh ca ngܩi nhn m thܩng qua cc Trm Phc V Th (mail servers).

 __________                                             ________
 | My-A |                                            | My-B |
 |--------|                                            |--------|
 | Spool  |                                            | Spool  |
 | Area   |                                            | Area   |
 |________|                      ______                |________|
	|    ______________     (      )      ______________  |
	|   |              |   (        )    |             |  |
	|___|  Mail Server |--( Internet  )--| Mail Server |__|
	    |       X      |   (        )    |     Y       |
	    |______________|    (______)     |_____________|
	Trm Phc V Th X            Trm Phc V Th Y

Nh hnh v pha trn cho thy, nu nh mt ngܩi my A gi ti mt ngܩi my B mt l th th trܧc nht my A s gi ljn Trm Phc V Th X (nu Trm Phc V Th X cn ang bn hoc b trc trc g th my A s tm thi b l th vo spool area v s tm cch gi sau). Khi Trm Phc V Th X nhn ܮc th t my A th X s chuyn tip cho Trm Phc V Th  Khi Trm Phc V Th Y nhn ܮc th t X th Y s chuyn th ti My B l no+i ngܩi nhn. Trܩng hp my B b trc trc th Trm Phc V Th Y s gi th v tm cch gi cho my B theo mt nh k trong ba ngy trܧc khi hon tr li cho ngܩi gi.

Thng thܩng th Trm Trm Phc V Th thܩng chuyn nhiu th cng mt lc cho mt my nhn. Nh th d trn Trm Trm Phc V Th Y c th chuyn nhiu th cng mt lc cho my B t nhiu ni gi ljn. Sau khi my B nhn tt c th t Trm Phc V Th Y ri my B s b th vo hp th ca ngܩi nhn. l l do gii thch ti sao thܩng thܩng ngܩi s dng nhn cng mt lc nhiu l th in gi t nhng ch khc nha

Mt vi cng dng khc ca Trm Phc V Th l khi ngܩi s dng c chuyn phi ngh mt thi gian th ngܩi s dng c th yu cu Trm Phc V Th gi gim tt c nhng th t trong thi gian ngܩi s dng vng mt hoc c th yu cu Trm Phc V Th chuyn tt c th t ti mt ci hp th khc.

IV - Cng Dng

Th t in t c rt nhiu cng dng v s nhanh chng v d dng s dng ca n. Mi ngܩi c th trao ǰi kin ti liu vi nhau trong thi gian tht ngn. Thng thܩng th t in t ch chuyn ti nhng ch 7-bits m thi nhng c Chng Trnh cho php ngܩi ta chuyn ti ti liu 8-bits bng cch phn tch v xp xp cc ti liu 8-bits ny thnh ti liu 7-bits. Sau khi chuyn ti ni nhn th ngܩi nhn dng Chng Trnh Th khc cn thit Nj chuyn ti liu 7-bits tr thnh 8-bits tr li. Ngoi ra, ngܩi ta cn dng th t in t Nj khin mt my t xa thi hnh mt hoc nhiu mnh lnh. Vi phng php ny ngܩi s dng c th gi th in cho mt my t xa yu cu my gi mt s ti liu tr v cho ngܩi s dng. Phng php ny gip cho ngܩi s dng khng cn phi trc tip lin lc vi my xa bng FTP Nj ly ti liu.

V - Bo Mt

S bo mt ca cc th t in t cn c nhiu khuyt im. Trong h thng my vi tnh, nhng ngܩi c chng mc ǥc bit vn c th džc th ca ngܩi khc trong bt c hp th no trn my. Ngoi ra th c th b džc ti cc Trm Phc V Th hoc trn ܩng trnh tnh trng ny, ngܩi s dng c th dng mt m Nj lm o ln v tr v mt ch Nj bo tn s b mt ca l th

VI - Tng Lai Ca E-Mail

in th ng mt vai tr quan trng trong ǩi sng khoa hc, kinh t, x hi, gio dc, v an ninh quc gi Ngy nay ngܩi ta trao ǰi vi nhau hng ngy nhng kin, ti liu vi nhau bng in th mc d cch xa nhau hng ngn cy s. C rt nhiu ngܩi tham gia vo Internet ch Nj gi/nha^.n th in t m th V in th da vo cu trc ca Internet cho nn n cng ngy cng bnh trܧng mt cch nhanh chng. Ngܩi ta khng ngng tm cch Nj khai thc ljn mc ti a v s hu dng ca n. Trong mt tng lai gn ngܩi ta c th lm cho in th c nhng kh nng sau:

- Mi bc th in s mang mt hnh chp ca ngܩi gi. Nh vy ngܩi nhn s bit ai gi th cho mnh.

- Ngܩi ta s dng in th Nj gi th vit bng ta C ngha l ngܩi nhn s džc th in m ngܩi nhn vit bng tay (hand writting). (Ch : Phn ny ܮc mt vi hng thng mi thc hnh nhng cha ܮc hon chnh lm)

- Thay v gi l th in bng ch, ngܩi gi c th dng in th Nj gi ting ni. Ngܩi nhn s lng nghe ܮc ging ni ca ngܩi gi khi nhn ܮc th

- Ngܩi gi c th gi mt cun phim hoc l nhng hnh nh lu Ƕng cho ngܩi nhn. (Ch : Hin gi ngܩi ta c th gi hnh nh bng in th nhng khng phi l hnh nh lu Ƕng.)

Trn y ch l vi th d in hnh m in th c th lm ܮc trong tng la Vi trnh Ƕ khoa hc k thut cao nh hin gi nhng vic trn s thc hin khng my kh khn. Nhng tr ngi ln nht hin gi l ܩng chuyn ti tn hiu ca Internet cn qu chm cho nn khng th no chuyn ti s lܮng khng l ca tn hiu. Ngoi ra cn tr ngi khc nh my tnh khng sc cha ht tt c tn hiu m n nhn ܮc. iu nn bit rng nhng m thanh (voice) v hnh nh (graphics) thܩng to ra nhng s lܮng tn hiu khng l.

Nhng lc gn y ngܩi ta bt u xy dng nhng ܩng chuyn ti cao tc trong Internet vi lu lܮng nhanh gp trm ngn ln so vi ܩng c. Hy vng vi tin trin nh vy, s c mt ngy mi ngܩi trn Internet s ܮc nhiu li ch v vic s dng din th

VII - Gii Thiu Nhng Chng Trnh Hu ch

Phn ln cc Chng Trnh Th NJu cho php ngܩi s dng quyt nh loi Chng Trnh Vit (editor) no Nj vit th in hoc džc th in. Ngܩi s dng c th li dng iu ny Nj dng ci Chng Trnh Vit no m h cm thy thnh tho nht. Ring i vi nhng ngܩi Vit s dng my vi tnh Nj vit in th c th xi nhng Chng Trnh c sn Nj vit v džc ting Vit. Hin nay, nhng Chng Trnh hu ch v thng dng ny ang ܮc ph bin mnh m trong cng ng ngܩi Vit trn khp th gii. Nhng Chng Trnh ny ܮc nghin cu v thc hin do nhm Nghin Cu Tiu Chun Ting Vit (Vietnamese Standardization Group - gi tt l Viet-Std) v nhm pht trin nhu liu TriChlor. Hai nhm ny quy t nhng chuyn vin u t tch cc trong vic xy dng mt b ch Vit trn my tnh. Nhng Chng Trnh do hai nhm ny thc hin c th chy (run) trn nhiu h thng khc nhau th d nh DOS, UNIX, WINDOWS. Ngoi nhng Chng Trnh rt hu dng , cn c rt nhiu ti liu, nhc phm, th vn v.v NJu ܮc ghi chp v lu tr cho mi ngܩi xi. iu ng khen ngi l v mc ch phc v qun chng Vietnam cho nn nhng Chng Trnh v tt c ti liu lu tr ny NJu min ph.

Phuong Thanh Nguyen
Network Routing Systems
Networking Systems
IBM, Research Triangle Park
E-Mail: pnguyen@vnet.ibm.com


Ti Liu Tham Kho:

- RFC-821: Postel, J. Simple Mail Transfer Protocol.
- RFC-974: Partridge, C. Mail routing and the domain system.
- RFC-1176: Crispin, M. Interactive Mail Access Protocol: Version 2.
- Internetworking with TCP/IP Vol.I Douglas  Comer, David L. Stevens


T ng tm dch:

Electronic mail: in th
System: H thng
Internet: Mng lܧi Truyn Tin Ton Cu
Computer: My vi tnh
Protocol: Nghi thc
Simple Mail Transfer Protocol: Nghi Thc n Gin Chuyn Vn Th T
User account: Chng mc
Modem: My bin iu/hoa`n iu
Mail Program: Chng Trnh Th
Operating System: H Thng iu Khin
Mail Address: a Ch Th T
user-mailbox: Hp-th
domain-part: khu-vng
Alias: Tn Hiu
Mail Forwarding: Cch Chuyn Tip Th
Send Mail: Chuyn Th
Receive Mail: Nhn Th
Mail Server: Trm Phc V Th


a Ch Lin Lc:

Nhm Viet_Std

Viet_std
1212 Somerset Drive
San Jose, CA 95132, USA

a ch in th: viet-std@haydn.stanford.edu
s in hnh th (fax): 408-246-9532

Nhm TriChlor

TriChlor
3388 Burgundy Drive
San Jose, CA 95132, USA

a ch in th: trichlor@haydn.stanford.edu
s in hnh th (fax): 408-246-9532