usenix.ps

早期freebsd实现

.39(Certain special cases can be han-)5.389 F 1.033(dled tri)72 603.6 R 1.033
(vially by)-.25 F F2 1.033(ad hoc)3.533 F F1 1.032(techniques, such as pro)
3.533 F 1.032(viding netw)-.15 F 1.032
(ork names that appear local to hosts on other)-.1 F(netw)72 615.6 Q 1.621
(orks, as with the Ethernet at Xerox P)-.1 F 4.121(ARC. Ho)-.92 F(we)-.25 E
-.15(ve)-.25 G 2.421 -.4(r, t).15 H 1.622(he general case is e).4 F 1.622
(xtremely comple)-.15 F 4.122(x. F)-.15 F(or)-.15 E -.15(ex)72 627.6 S .29
(ample, some netw).15 F .29(orks require that the route the message tak)-.1 F
.29(es be e)-.1 F .29(xplicitly speci\214ed by the sender)-.15 F 2.79(,s)-.4 G
(im-)490.11 627.6 Q 1.618(plifying the database update problem since only adja\
cent hosts must be entered into the system tables,)72 639.6 R .573(while other\
s use logical addressing, where the sender speci\214es the location of the rec\
ipient b)72 651.6 R .573(ut not ho)-.2 F 3.072(wt)-.25 G(o)499 651.6 Q 1.065
(get there.)72 663.6 R 1.065(Some netw)6.065 F 1.066(orks use a left-associati)
-.1 F 1.366 -.15(ve s)-.25 H 1.066(yntax and others use a right-associati).15 F
1.366 -.15(ve s)-.25 H 1.066(yntax, causing).15 F .32 LW 76 673.2 72 673.2 DL
80 673.2 76 673.2 DL 84 673.2 80 673.2 DL 88 673.2 84 673.2 DL 92 673.2 88
673.2 DL 96 673.2 92 673.2 DL 100 673.2 96 673.2 DL 104 673.2 100 673.2 DL 108
673.2 104 673.2 DL 112 673.2 108 673.2 DL 116 673.2 112 673.2 DL 120 673.2 116
673.2 DL 124 673.2 120 673.2 DL 128 673.2 124 673.2 DL 132 673.2 128 673.2 DL
136 673.2 132 673.2 DL 140 673.2 136 673.2 DL 144 673.2 140 673.2 DL 148 673.2
144 673.2 DL 152 673.2 148 673.2 DL 156 673.2 152 673.2 DL 160 673.2 156 673.2
DL 164 673.2 160 673.2 DL 168 673.2 164 673.2 DL 172 673.2 168 673.2 DL 176
673.2 172 673.2 DL 180 673.2 176 673.2 DL 184 673.2 180 673.2 DL 188 673.2 184
673.2 DL 192 673.2 188 673.2 DL 196 673.2 192 673.2 DL 200 673.2 196 673.2 DL
204 673.2 200 673.2 DL 208 673.2 204 673.2 DL 212 673.2 208 673.2 DL 216 673.2
212 673.2 DL/F3 8/Times-Roman@0 SF .556(*A considerable part of this w)93.6
685.2 R .556(ork w)-.08 F .556(as done while under the emplo)-.08 F 2.557(yo)
-.08 G 2.557(ft)323.107 685.2 S .557(he INGRES Project at the Uni)330.552 685.2
R -.12(ve)-.2 G .557(rsity of California at).12 F(Berk)72 694.8 Q(ele)-.08 E
-.52(y.)-.12 G/F4 10/Times-Bold@0 SF(Mail Systems and Addr)72 756 Q
(essing in 4.2bsd)-.18 E(1)499 756 Q EP
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/F0 10/Times-Bold@0 SF(Mail Systems and Addr)72 60 Q(essing in 4.2bsd)-.18 E(2)
499 60 Q/F1 10/Times-Roman@0 SF(ambiguity in mix)72 96 Q(ed addresses.)-.15 E
.679(Internet standards seek to eliminate these problems.)97 112.2 R(Initially)
5.678 E 3.178(,t)-.65 G .678(hese proposed e)353.138 112.2 R .678
(xpanding the address)-.15 F .331
(pairs to address triples, consisting of {netw)72 124.2 R .331
(ork, host, username} triples.)-.1 F(Netw)5.332 E .332(ork numbers must be uni)
-.1 F -.15(ve)-.25 G -.2(r-).15 G 1.452
(sally agreed upon, and hosts can be assigned locally on each netw)72 136.2 R
3.952(ork. The)-.1 F(user)3.952 E(-le)-.2 E -.15(ve)-.25 G 3.952(lp).15 G 1.452
(resentation w)440.718 136.2 R(as)-.1 E .249(changed to address domains, compr\
ised of a local resource identi\214cation and a hierarchical domain speci\214-)
72 148.2 R 1.54(cation with a common static root.)72 160.2 R 1.539
(The domain technique separates the issue of ph)6.539 F 1.539(ysical v)-.05 F
1.539(ersus logical)-.15 F 3.001(addressing. F)72 172.2 R .501(or e)-.15 F .502
(xample, an address of the form \[e-mail])-.15 F(ele)-.1 E -.65(y.)
-.15 G .502(arpa\232 describes the logical or).65 F -.05(ga)-.18 G(niza-).05 E
.443(tion of the address space \(user \231eric\232 on host \231a\232 in the Co\
mputer Center at Berk)72 184.2 R(ele)-.1 E .443(y\) b)-.15 F .443
(ut not the ph)-.2 F(ysical)-.05 E(netw)72 196.2 Q .934(orks used \(for e)-.1 F
.934(xample, this could go o)-.15 F -.15(ve)-.15 G 3.434(rd).15 G(if)274.722
196.2 Q .934(ferent netw)-.25 F .935
(orks depending on whether \231a\232 were on an)-.1 F
(ethernet or a store-and-forw)72 208.2 Q(ard netw)-.1 E(ork\).)-.1 E/F2 10
/Times-Italic@0 SF(Sendmail)97 224.4 Q F1 .493
(is intended to help bridge the g)2.993 F .493(ap between the totally)-.05 F F2
.493(ad hoc)2.993 F F1 -.1(wo)2.993 G .493(rld of netw).1 F .493(orks that kno)
-.1 F(w)-.25 E .854(nothing of each other and the clean, tightly-coupled w)72
236.4 R .854(orld of unique netw)-.1 F .855(ork numbers.)-.1 F .855
(It can accept old)5.855 F .633(arbitrary address syntax)72 248.4 R .632(es, r\
esolving ambiguities using heuristics speci\214ed by the system administrator)
-.15 F 3.132(,a)-.4 G(s)500.11 248.4 Q .347(well as domain-based addressing.)72
260.4 R .347(It helps guide the con)5.347 F -.15(ve)-.4 G .347
(rsion of message formats between disparate net-).15 F -.1(wo)72 272.4 S 3.395
(rks. In).1 F(short,)3.395 E F2(sendmail)3.395 E F1 .894
(is designed to assist a graceful transition to consistent internetw)3.395 F
.894(ork addressing)-.1 F(schemes.)72 284.4 Q .689
(Section 1 de\214nes some of the terms frequently left fuzzy when w)97 312.6 R
.69(orking in mail systems.)-.1 F .69(Section 2)5.69 F .595
(discusses the design goals for)72 324.6 R F2(sendmail)3.095 E F1 5.595(.I)C
3.095(ns)243.33 324.6 S .595(ection 3, the ne)255.315 324.6 R 3.095(wa)-.25 G
.594(ddress formats and basic features of)332.705 324.6 R F2(send-)3.094 E
(mail)72 336.6 Q F1 .893(are described.)3.393 F .893
(Section 4 discusses some of the special problems of the UUCP netw)5.893 F
3.394(ork. The)-.1 F(dif)3.394 E(fer)-.25 E(-)-.2 E(ences between)72 348.6 Q F2
(sendmail)2.5 E F1(and)2.5 E F2(delivermail)2.5 E F1
(are presented in section 5.)2.5 E F0(DISCLAIMER:)112 376.8 Q F1 3.333(An)3.333
G .833(umber of e)199.216 376.8 R .832
(xamples in this paper use names of actual people and)-.15 F(or)112 388.8 Q
-.05(ga)-.18 G 4.572(nizations. This).05 F 2.072
(is not intended to imply a commitment or e)4.572 F -.15(ve)-.25 G 4.573(na).15
G 4.573(ni)409.987 388.8 S(ntellectual)422.34 388.8 Q 1.094
(agreement on the part of these people or or)112 400.8 R -.05(ga)-.18 G 3.594
(nizations. In).05 F(particular)3.594 E 3.594(,B)-.4 G 1.094(ell T)408.896
400.8 R(elephone)-.7 E .656
(Laboratories \(BTL\), Digital Equipment Corporation \(DEC\), La)112 412.8 R
.657(wrence Berk)-.15 F(ele)-.1 E 3.157(yL)-.15 G(abo-)446.23 412.8 Q 2.136
(ratories \(LBL\), Britton-Lee Incorporated \(BLI\), and the Uni)112 424.8 R
-.15(ve)-.25 G 2.136(rsity of California at).15 F(Berk)112 436.8 Q(ele)-.1 E
3.088(ya)-.15 G .588(re not committed to an)155.378 436.8 R 3.089(yo)-.15 G
3.089(ft)261.219 436.8 S .589(hese proposals at this time.)270.418 436.8 R .589
(Much of this paper)5.589 F
(represents no more than the personal opinions of the author)112 448.8 Q(.)-.55
E F0 2.5(1. DEFINITIONS)72 477 R F1 .266(There are four basic concepts that mu\
st be clearly distinguished when dealing with mail systems:)112 493.2 R .514
(the user \(or the user')87 505.2 R 3.014(sa)-.55 G .515(gent\), the user')
182.6 505.2 R 3.015(si)-.55 G .515(denti\214cation, the user')253.025 505.2 R
3.015(sa)-.55 G .515(ddress, and the route.)354.56 505.2 R .515(These are dis-)
5.515 F(tinguished primarily by their position independence.)87 517.2 Q F0 2.5
(1.1. User)87 541.2 R(and Identi\214cation)2.5 E F1 .264
(The user is the being \(a person or program\) that is creating or recei)127
557.4 R .263(ving a message.)-.25 F(An)5.263 E F2 -.1(age)2.763 G(nt).1 E F1
.659(is an entity operating on behalf of the user \212 such as a secretary who\
 handles my mail.)102 569.4 R .66(or a pro-)5.66 F(gram that automatically ret\
urns a message such as \231I am at the UNICOM conference.)102 581.4 Q<9a>-.7 E
.931(The identi\214cation is the tag that goes along with the particular user)
127 597.6 R 5.931(.T)-.55 G .931(his tag is completely)418.707 597.6 R .216
(independent of location.)102 609.6 R -.15(Fo)5.216 G 2.716(re).15 G .216
(xample, my identi\214cation is the string \231Eric Allman,)225.324 609.6 R
2.717<9a61>-.7 G .217(nd this identi-)448.006 609.6 R 1.228
(\214cation does not change whether I am located at U.C. Berk)102 621.6 R(ele)
-.1 E 2.527 -.65(y, a)-.15 H 3.727(tB).65 G 1.227
(ritton-Lee, or at a scienti\214c)390.502 621.6 R(institute in Austria.)102
633.6 Q 2.379
(Since the identi\214cation is frequently ambiguous \(e.g., there are tw)127
649.8 R 4.879<6f99>-.1 G 2.38(Robert Henry\232s at)426.48 649.8 R(Berk)102
661.8 Q(ele)-.1 E .316(y\) it is common to add other disambiguating informatio\
n that is not strictly part of the iden-)-.15 F
(ti\214cation \(e.g., Robert \231Code Generator\232 Henry v)102 673.8 Q
(ersus Robert \231System Administrator\232 Henry\).)-.15 E F0 -1(Ve)72 756 S
(rsion 8.2)1 E(USENIX \255 J)249.805 756 Q(an 83)-.15 E(Last Mod 11/27/93)
424.55 756 Q EP
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/F0 10/Times-Bold@0 SF(Mail Systems and Addr)72 60 Q(essing in 4.2bsd)-.18 E(3)
499 60 Q 2.5(1.2. Addr)87 96 R(ess)-.18 E/F1 10/Times-Roman@0 SF .785
(The address speci\214es a location.)127 112.2 R .786(As I mo)5.786 F 1.086
-.15(ve a)-.15 H .786(round, my address changes.).15 F -.15(Fo)5.786 G 3.286
(re).15 G .786(xample, my)455.994 112.2 R 9.712
(address might change from \231eric@Berk)102 124.2 R(ele)-.1 E -.65(y.)-.15 G
(ARP).65 E 9.711(A\232 to \[e-mail]\232 or \231all-)-.92 F
([e-mail]\232 depending on my current af)102 136.2 Q(\214liation.)-.25
E(Ho)127 152.4 Q(we)-.25 E -.15(ve)-.25 G 2.819 -.4(r, a).15 H 4.519(na).4 G
2.019(ddress is independent of the location of an)188.018 152.4 R 2.019
(yone else.)-.15 F 2.02(That is, my address)7.02 F .385(remains the same to e)
102 164.4 R -.15(ve)-.25 G .385(ryone who might be sending me mail.).15 F -.15
(Fo)5.385 G 2.885(re).15 G .385(xample, a person at MIT and a)379.22 164.4 R
(person at USC could both send to \231eric@Berk)102 176.4 Q(ele)-.1 E -.65(y.)
-.15 G(ARP).65 E(A\232 and ha)-.92 E .3 -.15(ve i)-.2 H 2.5(ta).15 G(rri)388.44
176.4 Q .3 -.15(ve t)-.25 H 2.5(ot).15 G(he same mailbox.)422.48 176.4 Q .627
(Ideally a \231white pages\232 service w)127 192.6 R .627(ould be pro)-.1 F
.627(vided to map user identi\214cations into addresses)-.15 F .444(\(for e)102
204.6 R .444(xample, see [Solomon81]\).)-.15 F .444
(Currently this is handled by passing around scraps of paper or by)5.444 F
(calling people on the telephone to \214nd out their address.)102 216.6 Q F0
2.5(1.3. Route)87 240.6 R F1 .288(While an address speci\214es)127 256.8 R/F2
10/Times-Italic@0 SF(wher)2.788 E(e)-.37 E F1 .289
(to \214nd a mailbox, a route speci\214es)2.789 F F2(how)2.789 E F1 .289
(to \214nd the mailbox.)2.789 F(Speci\214cally)102 268.8 Q 2.607(,i)-.65 G
2.607(ts)156.457 268.8 S .106(peci\214es a path from sender to recei)165.734
268.8 R -.15(ve)-.25 G 3.706 -.55(r. A).15 H 2.606(ss).55 G .106
(uch, the route is potentially dif)343.364 268.8 R .106(ferent for)-.25 F -2.15
-.25(ev e)102 280.8 T(ry pair of people in the electronic uni).25 E -.15(ve)
-.25 G(rse.).15 E .258(Normally the route is hidden from the user by the softw)
127 297 R 2.758(are. Ho)-.1 F(we)-.25 E -.15(ve)-.25 G 1.058 -.4(r, s).15 H
.258(ome netw).4 F .258(orks put the)-.1 F -.2(bu)102 309 S 1.972
(rden of determining the route onto the sender).2 F 6.971(.A)-.55 G 1.971
(lthough this simpli\214es the softw)322.544 309 R 1.971(are, it also)-.1 F
(greatly impairs the usability for most users.)102 321 Q(The UUCP netw)5 E
(ork is an e)-.1 E(xample of such a netw)-.15 E(ork.)-.1 E F0 2.5(2. DESIGN)72
345 R(GO)2.5 E(ALS)-.4 E F1(Design goals for)112 363.2 Q F2(sendmail)2.5 E/F3 7
/Times-Roman@0 SF(1)216.71 359.2 Q F1(include:)222.71 363.2 Q 12.5
(\(1\) Compatibility)92 379.4 R 1.363(with the e)3.863 F 1.363
(xisting mail programs, including Bell v)-.15 F 1.363(ersion 6 mail, Bell v)
-.15 F 1.364(ersion 7)-.15 F 3.589(mail, Berk)118.66 391.4 R(ele)-.1 E(y)-.15 E
F2(Mail)6.089 E F1 3.589
([Shoens79], BerkNet mail [Schmidt79], and hopefully UUCP mail)6.089 F([No)
118.66 403.4 Q 2.5(witz78]. ARP)-.25 F(ANET mail [Crock)-.92 E(er82] w)-.1 E
(as also required.)-.1 E 12.5(\(2\) Reliability)92 419.6 R 4.002(,i)-.65 G
4.002(nt)169.522 419.6 S 1.502(he sense of guaranteeing that e)181.304 419.6 R
-.15(ve)-.25 G 1.502(ry message is correctly deli).15 F -.15(ve)-.25 G 1.503
(red or at least).15 F .368
(brought to the attention of a human for correct disposal; no message should e)
118.66 431.6 R -.15(ve)-.25 G 2.868(rb).15 G 2.868(ec)452.252 431.6 S
(ompletely)464 431.6 Q 2.54(lost. This)118.66 443.6 R .04(goal w)2.54 F .041
(as considered essential because of the emphasis on mail in our en)-.1 F 2.541
(vironment. It)-.4 F 1.755
(has turned out to be one of the hardest goals to satisfy)118.66 455.6 R 4.254
(,e)-.65 G 1.754(specially in the f)363.756 455.6 R 1.754(ace of the man)-.1 F
(y)-.15 E .977(anomalous message formats produced by v)118.66 467.6 R .977
(arious ARP)-.25 F .977(ANET sites.)-.92 F -.15(Fo)5.977 G 3.478(re).15 G .978
(xample, certain sites)420.114 467.6 R .069
(generate improperly formated addresses, occasionally causing error)118.66
479.6 R .069(-message loops.)-.2 F .068(Some hosts)5.069 F .766(use blanks in \
names, causing problems with mail programs that assume that an address is one)
118.66 491.6 R -.1(wo)118.66 503.6 S 3.924(rd. The).1 F 1.423
(semantics of some \214elds are interpreted slightly dif)3.923 F 1.423
(ferently by dif)-.25 F 1.423(ferent sites.)-.25 F(In)6.423 E(summary)118.66
515.6 Q 3.022(,t)-.65 G .523(he obscure features of the ARP)163.532 515.6 R
.523(ANET mail protocol really)-.92 F F2(ar)3.023 E(e)-.37 E F1 .523
(used and are dif)3.023 F(\214cult)-.25 E(to support, b)118.66 527.6 Q
(ut must be supported.)-.2 E 12.5(\(3\) Existing)92 543.8 R(softw)2.939 E .439
(are to do actual deli)-.1 F -.15(ve)-.25 G .439(ry should be used whene).15 F
-.15(ve)-.25 G 2.938(rp).15 G 2.938(ossible. This)387.658 543.8 R .438
(goal deri)2.938 F -.15(ve)-.25 G 2.938(sa).15 G(s)500.11 543.8 Q
(much from political and practical considerations as technical.)118.66 555.8 Q
12.5(\(4\) Easy)92 572 R -.15(ex)2.898 G .398(pansion to f).15 F .398
(airly comple)-.1 F 2.898(xe)-.15 G -.4(nv)261.06 572 S .399
(ironments, including multiple connections to a single net-).4 F -.1(wo)118.66
584 S .63(rk type \(such as with multiple UUCP or Ethernets\).).1 F .63
(This goal requires consideration of the)5.63 F
(contents of an address as well as its syntax in order to determine which g)
118.66 596 Q(ate)-.05 E -.1(wa)-.25 G 2.5(yt).1 G 2.5(ou)443.48 596 S(se.)
455.98 596 Q 12.5(\(5\) Con\214guration)92 612.2 R 1.048
(information should not be compiled into the code.)3.548 F 3.549(As)6.049 G
1.049(ingle compiled program)405.802 612.2 R .084
(should be able to run as is at an)118.66 624.2 R 2.584(ys)-.15 G .083
(ite \(barring such basic changes as the CPU type or the operat-)256.196 624.2
R .342(ing system\).)118.66 636.2 R 1.942 -.8(We h)5.342 H -2.25 -.2(av e).8 H
.343(found this seemingly unimportant goal to be critical in real life.)3.042 F
(Besides)5.343 E .734(the simple problems that occur when an)118.66 648.2 R
3.234(yp)-.15 G .734(rogram gets recompiled in a dif)295.568 648.2 R .733
(ferent en)-.25 F(vironment,)-.4 E(man)118.66 660.2 Q 2.5(ys)-.15 G(ites lik)
147.12 660.2 Q 2.5(et)-.1 G 2.5<6f99>183.69 660.2 S(\214ddle\232 with an)195.63
660.2 Q(ything that the)-.15 E 2.5(yw)-.15 G(ill be recompiling an)327.27 660.2
Q(yw)-.15 E(ay)-.1 E(.)-.65 E .32 LW 76 678.8 72 678.8 DL 80 678.8 76 678.8 DL
84 678.8 80 678.8 DL 88 678.8 84 678.8 DL 92 678.8 88 678.8 DL 96 678.8 92
678.8 DL 100 678.8 96 678.8 DL 104 678.8 100 678.8 DL 108 678.8 104 678.8 DL
112 678.8 108 678.8 DL 116 678.8 112 678.8 DL 120 678.8 116 678.8 DL 124 678.8
120 678.8 DL 128 678.8 124 678.8 DL 132 678.8 128 678.8 DL 136 678.8 132 678.8
DL 140 678.8 136 678.8 DL 144 678.8 140 678.8 DL 148 678.8 144 678.8 DL 152
678.8 148 678.8 DL 156 678.8 152 678.8 DL 160 678.8 156 678.8 DL 164 678.8 160
678.8 DL 168 678.8 164 678.8 DL 172 678.8 168 678.8 DL 176 678.8 172 678.8 DL
180 678.8 176 678.8 DL 184 678.8 180 678.8 DL 188 678.8 184 678.8 DL 192 678.8
188 678.8 DL 196 678.8 192 678.8 DL 200 678.8 196 678.8 DL 204 678.8 200 678.8
DL 208 678.8 204 678.8 DL 212 678.8 208 678.8 DL 216 678.8 212 678.8 DL/F4 5
/Times-Roman@0 SF(1)93.6 689.2 Q/F5 8/Times-Roman@0 SF(This section mak)3.2 I
(es no distinction between)-.08 E/F6 8/Times-Italic@0 SF(delivermail)2 E F5
(and)2 E F6(sendmail.)2 E F0 -1(Ve)72 756 S(rsion 8.2)1 E(USENIX \255 J)249.805
756 Q(an 83)-.15 E(Last Mod 11/27/93)424.55 756 Q EP
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/F0 10/Times-Bold@0 SF(Mail Systems and Addr)72 60 Q(essing in 4.2bsd)-.18 E(4)
499 60 Q/F1 10/Times-Roman@0 SF(\(6\))92 96 Q/F2 10/Times-Italic@0 SF(Sendmail)
118.66 96 Q F1 .184(must be able to let v)2.684 F .184
(arious groups maintain their o)-.25 F .184(wn mailing lists, and let indi)-.25
F(viduals)-.25 E(specify their o)118.66 108 Q(wn forw)-.25 E
(arding, without modifying the system alias \214le.)-.1 E 12.5(\(7\) Each)92
124.2 R .313(user should be able to specify which mailer to e)2.814 F -.15(xe)
-.15 G .313(cute to process mail being deli).15 F -.15(ve)-.25 G .313(red for)
.15 F 3.098(him. This)118.66 136.2 R .598(feature allo)3.098 F .598
(ws users who are using specialized mailers that use a dif)-.25 F .598