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** "Creator" brian
** "Creation Date" Sat May  4 18:52:16 2002
** "Creation Version" 4.42 (1021.500)
** "Revisor" brian
** "Last Modified" Wed May 19 20:17:19 2004
** "Last Modified Version" 4.42 (1021.500)

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  browse rejected mail"
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   "As soon as the sender connects, you know their IP address, whic
 h can't be forged"
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 main.com>\n550 rejected because 192.0.2.1 is in a black list at 
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   "Disadvantages of RBLs"
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  .STR
   "RBLs are always under legal threats from spammers; they come an
 d go"
  .STR
   "\nWon't catch all spam"
  .STR
   "\nNot effective against viruses or joe-jobs"
END PICTURE
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  .STR
   "Choosing which blacklists to use"
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   "Many are free, some are not"
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   "\n\te.g. mail-abuse.org"
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   "\n\tPolicies are too draconian; you end up losing connectivity 
 to people you want"
  .STR
   "\n\tSomeone else's policy may not be good for you (e.g. a list 
 which blocks all Nigerian address space is not useful for an Afr
 ican ISP)"
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   SIZE 320000
   "\nTry these:"
  .STR
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   "\nsbl.spamhaus.org (known spammers)"
  .STR
   "\n\trelays.ordb.org (open relays)"
  .STR
   "\n\tbl.spamcop.net (dynamic spam sources)"
END PICTURE
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  T_PNTS (0,449)(0,0)(8659,0)(8659,581)(0,581)(0,449)(8659,449)
  .STR
   "Configuring blacklists in Exim"
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 T_POS <105 1562 9892 7370>
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  T_PNTS (0,323)(0,0)(9154,0)(9154,866)(0,866)(0,323)(9154,323)
  .STR
   "Easy: uncomment two lines in the configure file and customise t
 o your chosen lists"
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 RECOLOR ON
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 H_SPACE 0
 .STR
  "deny    message    = rejected because $sender_host_address is i
 n a black list \\\n                                    at $dnsli
 st_domain\\n$dnslist_text \n            dnslists      = sbl.spam
 haus.org : relays.ordb.org : bl.spamcop.net \n"
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 T_PNTS (0,323)(0,0)(9244,0)(9244,1748)(0,1748)(0,323)(9244,323)
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 .STR
  "If your users are in a database, it's possible with some config
 uration work to use different dnslists for each user (opt-in, op
 t-out, choice of policies)"
END PICTURE
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END NOTES

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  TXTXYOFF <-4 437>
  T_PNTS (0,437)(0,0)(9114,0)(9114,569)(0,569)(0,437)(9114,437)
  .STR
   "Testing blacklists with exim -bh"
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 T_POS <105 1562 9892 7370>
 .TXT AT (76,1663)
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  T_PNTS (0,326)(0,0)(9201,0)(9201,2089)(0,2089)(0,326)(9201,326)
  .STR
   "exim -bh x.x.x.x sets up a pretend SMTP session as if it were f
 rom address x.x.x.x"
  .STR
   "\nMany lists have test IP addresses which will definitely rejec
 t - e.g. 127.0.0.2"
.TXT AT (0,4001)
 RECOLOR ON
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  L_SPACE 250 MARGINS <125 125 250 62>
  "#"
 .STR
  BOLD ON L_SPACE 292 MARGINS <146 146 292 73>
  " /usr/exim/bin/exim -bh 127.0.0.2 \n "
 .STR
  BOLD OFF
  "\n**** SMTP testing session as if from host 127.0.0.2 \n**** Th
 is is not for real! \n220 noc.t1.ws.afnog.org ESMTP Exim 4.34 We
 d, 19 May 2004 10:26:40\n"
 .STR
  BOLD ON
  "mail from"
 .STR
  ":<> "
 .STR
  BOLD OFF
  "\n250 OK \n"
 .STR
  BOLD ON
  "rcpt to:<inst@noc.t1.ws.afnog.org> "
 .STR
  BOLD OFF
  "\n550-rejected because 127.0.0.2 is in a black list at sbl.spam
 haus.org \n550 http://www.spamhaus.org/SBL/sbl.lasso?query=SBL23
 3 \n"
 .STR
  BOLD ON
  "quit"
 .STR
  BOLD OFF
  "\n221 noc.t1.ws.afnog.org closing connection"
END PICTURE
NOTES
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  T_PNTS (0,439)(0,0)(6567,0)(6567,1182)(0,1182)(0,439)(6567,439)
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  .STR
   "Ways to identify spam:\n2. By content"
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  .STR
   "Look for phrases which typically occur in spam"
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   "\nGood systems also look for phrases which typically "
  .STR
   ITALICS ON
   "don't"
  .STR
   ITALICS OFF
   " occur in spam to reduce false positives"
  .STR
   "\nThe balance between these two indicates whether it's spam (an
 d how sure we are)"
END PICTURE
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  .STR
   "Spammers are sad and predictable"
  .STR
   "\nIf you paid a human to delete spam, they could recognise it e
 asily"
  .STR
   "\nDoesn't matter where it came from: spam is spam"
END PICTURE
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   "Disadvantages of content filtering"
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   "\nIt's an arms race: as filters match particular patterns, spam
 mers change their behaviour"
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   "\n\tUnless rules are customised for each user, but then it's mo
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   "Apply the exiscan-acl patch "
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   "\n\thttp://duncanthrax.net/exiscan-acl/"
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   "\nInstall spamassassin and run spamd"
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   "\n\thttp://www.spamassassin.org/"
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   "\nSet up an ACL to check the "
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   ITALICS ON
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   ITALICS OFF
   " of the mail and either reject or add a warning header"
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   "\nU"
  .STR
   "pdate spamassassin rules regularly"
  .STR
   "\nNot trivial to implement"
END PICTURE
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   " filtering"
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  .STR
   "Given a sample of messages which are known to be \"spam\" or \"
 not spam\", builds a map of which words occur more often in one 
 than the other"
  .STR
   "\nThe \"not spam\" profile is different for everyone, and there
 fore much harder for spammers to guess"
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   "\nFilter is very effective, but needs ongoing \"training\" for 
 mails which slip through"
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  "See "
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  "http://www.paulgraham.com/spam.html"
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  T_PNTS (0,439)(0,0)(6567,0)(6567,1065)(0,1065)(0,439)(6567,439)
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  .STR
   "Ways to identify spam:\n3. Whitelists"
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  T_PNTS (0,326)(0,0)(9287,0)(9287,3219)(0,3219)(0,326)(9287,326)
  .STR
   "Only accept mail from people we already know "
  .STR
   "\nActually, spammers could forge messages which appear to be fr
 om people we know"
  .STR
   "\nBut for now, they don't seem to be collecting information on 
 who we associate with"
END PICTURE
NOTES
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END NOTES

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  T_PNTS (0,439)(0,0)(9148,0)(9148,1061)(0,1061)(0,439)(9148,439)
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   "Receiving mail from people not on our whitelist"
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  T_PNTS (0,323)(0,0)(9272,0)(9272,4901)(0,4901)(0,323)(9272,323)
  .STR
   "By password: e.g. if they include a magic word in the Subject: 
 header"
  .STR
   "\nBy content filtering: e.g. if they pass spamassassin with a v
 ery low spam score"
  .STR
   "\nChallenge-response systems put the mail in a hold queue and s
 end back a message"
  .STR
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   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tIf the person responds, they are assumed to be OK and are w
 hitelisted."
  .STR
   "\n\tOne day soon, spammers will build robots to do this :-("
END PICTURE
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END NOTES

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  TXTXYOFF <1 439>
  T_PNTS (0,439)(0,0)(7111,0)(7111,571)(0,571)(0,439)(7111,439)
  .STR
   "Advantages of whitelists"
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  TXTXYOFF <11 326>
  T_PNTS (0,326)(0,0)(8907,0)(8907,2534)(0,2534)(0,326)(8907,326)
  .STR
   "Currently very effective at blocking spam and viruses"
  .STR
   "\nOnce we have established communication with someone, the prob
 ability of a future false positive is very low"
END PICTURE
NOTES
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END NOTES

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  TXTXYOFF <-44 439>
  T_PNTS (0,439)(0,0)(7912,0)(7912,571)(0,571)(0,439)(7912,439)
  .STR
   "Disadvantages of whitelists"
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 TEMPLATE_FLAGS <2 3 0 0>
 T_POS <105 1562 9892 7370>
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  T_PNTS (0,323)(0,0)(9078,0)(9078,5348)(0,5348)(0,323)(9078,323)
  .STR
   "Makes it difficult or annoying for people we don't know to cont
 act us for the first time"
  .STR
   "\nOn a server-side solution, each user needs a separate whiteli
 st and a way to edit it"
  .STR
   "\nAutomatically w"
  .STR
   "hitelisting people we sent mail TO is tricky if done server-sid
 e"
  .STR
   "\nChallenge-response systems are difficult to deploy in a scala
 ble way"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\thttp://www.tmda.net/"
  .STR
   "\n\thttp://www.paganini.net/ask/"
END PICTURE
NOTES
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END NOTES

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  TXTXYOFF <-129 439>
  T_PNTS (0,439)(0,0)(8100,0)(8100,1177)(0,1177)(0,439)(8100,439)
  .STR
   "Disadvantages of whitelists (cont.)"
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  PARA <-500 500 -500 1 1000 0 3 108>
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  SIZE 320000 BOLD OFF HOR_JUST LEFT L_SPACE 444
  TXTXYOFF <11 326>
  T_PNTS (0,326)(0,0)(9302,0)(9302,5663)(0,5663)(0,326)(9302,326)
  .STR
   "If filtering at the MAIL FROM stage, beware that for many peopl
 e the envelope sender is different to the From: address they put
  in their headers"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tMAIL FROM could even be different for every message they se
 nd (VERP: Variable Envelope Return Path)"
  .STR
   PARA <-500 500 -500 1 1000 0 3 108>
   V_SPACE <333 444 0>
   SIZE 320000
   "\nChallenge-response systems can interact badly with mailing li
 sts"
  .STR
   "\nBig risk of losing legitimate bounces"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tBounces are an important part of the integrity of E-mail"
END PICTURE
NOTES
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END NOTES

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 TEMPLATE_FLAGS <1 0 0 0>
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 .TXT AT (1115,235)
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  SIZE 440000 BOLD ON HOR_JUST CENTER L_SPACE 611 MARGINS <0 0 0 0>
  TXTXYOFF <-44 439>
  T_PNTS (0,439)(0,0)(7726,0)(7726,571)(0,571)(0,439)(7726,439)
  .STR
   "BAD ways to identify spam"
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  T_PNTS (0,326)(0,0)(9254,0)(9254,5864)(0,5864)(0,326)(9254,326)
  .STR
   "Checking the domain of MAIL FROM:<...> or doing a callback to c
 heck the whole address"
  .STR
   "\nComparing the domain in MAIL FROM to the IP address the messa
 ge came from (SPF)"
  .STR
   "\nChecking whether the message is correctly formatted according
  to RFC rules, etc"
  .STR
   "\nThese rules might catch some spam, today (until the spammers 
 adapt). But there are also plenty of badly-configured systems be
 longing to non-spammers. You WILL lose mail that you wanted to r
 eceive."
END PICTURE
NOTES
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  TXTXYOFF <-39 439>
  T_PNTS (0,439)(0,0)(5316,0)(5316,571)(0,571)(0,439)(5316,439)
  .STR
   "Identifying viruses"
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 T_POS <105 1562 9892 7370>
 .TXT AT (64,1658)
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  TXTXYOFF <11 318>
  T_PNTS (0,318)(0,0)(8610,0)(8610,4481)(0,4481)(0,318)(8610,318)
  .STR
   "Recent volume has increased massively"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
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   "\n\tUsers happily open and run attachments on mails from strang
 ers!"
  .STR
   PARA <-500 500 -500 1 1000 0 3 108>
   V_SPACE <333 444 0>
   SIZE 320000
   "\nLike spam, current viruses have forged envelope sender and he
 aders"
  .STR
   "\nNaive implementation might block all attachments with executa
 ble extensions"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tBlocks too many legitimate uses of E-mail"
  .STR
   "\n\tSome viruses come in .zip files now"
END PICTURE
NOTES
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END NOTES

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  TXTXYOFF <-39 439>
  T_PNTS (0,439)(0,0)(6209,0)(6209,571)(0,571)(0,439)(6209,439)
  .STR
   "Identifying viruses (2)"
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 RECOLOR ON
 TEMPLATE_FLAGS <2 3 0 0>
 T_POS <105 1562 9892 7370>
 .TXT AT (74,1663)
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  TXTXYOFF <11 323>
  T_PNTS (0,323)(0,0)(9079,0)(9079,5362)(0,5362)(0,323)(9079,323)
  .STR
   "The only sure-fire way is content filtering: matching attachmen
 ts against \"signatures\" (patterns) of known viruses"
  .STR
   "\nMany solutions are commercial, expensive, cost increases with
  number of users"
  .STR
   "\nSome are free, e.g. clamav"
  .STR
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   SIZE 280000
   "\n\thttp://clamav.sourceforge.net/"
  .STR
   "\n\tCall it from exim using exiscan-acl (see before)"
  .STR
   PARA <-500 500 -500 1 1000 0 3 108>
   V_SPACE <333 444 0>
   SIZE 320000
   "\nNew viruses are written all the time, signatures need updatin
 g very frequently"
END PICTURE
NOTES
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END NOTES

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  TXTXYOFF <-64 437>
  T_PNTS (0,437)(0,0)(2943,0)(2943,569)(0,569)(0,437)(2943,437)
  .STR
   "\"Joe-jobs\""
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  TXTXYOFF <11 318>
  T_PNTS (0,318)(0,0)(8346,0)(8346,861)(0,861)(0,318)(8346,318)
  .STR
   "A spammer or virus sends out mail with forged envelope sender"
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 RECOLOR ON
 T_PNTS (0,318)(0,0)(9184,0)(9184,2970)(0,2970)(0,318)(9184,318)
 .STR
  "The message is accepted by some intermediate mailer, and later 
 bounces (e.g. non-existent recipient, user over quota, virus det
 ected)\nThe bounce goes to <innocent-user> who had nothing to do
  with it"
.TXT AT (32,2748)
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 TXTXYOFF <0 0>
 PNTS (0,0)(10000,0)(10000,1001)(0,1001)(0,0)
 H_SPACE 0
 .STR
  L_SPACE 250 MARGINS <125 125 250 62>
  "MAIL FROM:<innocent-user@example.com>\nRCPT TO:<target@target-d
 omain.com>"
END PICTURE
NOTES
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END NOTES

SLIDE_INFO
 SLIDE_STYLE <0 -1 1>
 LAYOUT_ID <1 2 12 12 12>
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 RECOLOR ON
 TEMPLATE_FLAGS <1 0 0 0>
 T_POS <105 85 9892 1504>
 .TXT AT (364,242)
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  SIZE 440000 BOLD ON HOR_JUST CENTER L_SPACE 611 MARGINS <0 0 0 0>
  TXTXYOFF <-129 439>
  T_PNTS (0,439)(0,0)(9450,0)(9450,1061)(0,1061)(0,439)(9450,439)
  H_SPACE 9788
  .STR
   "Difficulties with blocking joe-job bounces"
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 T_POS <105 1562 9892 7370>
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  TXTXYOFF <11 318>
  T_PNTS (0,318)(0,0)(9275,0)(9275,5763)(0,5763)(0,318)(9275,318)
  .STR
   "All bounces have empty envelope sender, MAIL FROM:<>"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tNot any use for filtering"
  .STR
   PARA <-500 500 -500 1 1000 0 3 108>
   V_SPACE <333 444 0>
   SIZE 320000
   "\nJoe-job bounces are genuine MTA bounces - just not to message
 s that "
  .STR
   ITALICS ON
   "we"
  .STR
   ITALICS OFF
   " sent"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tcontent filtering to identify a bounce doesn't help"
  .STR
   PARA <-500 500 -500 1 1000 0 3 108>
   V_SPACE <333 444 0>
   SIZE 320000
   "\nDiscarding all bounces is definitely not an option"
  .STR
   PARA <-500 1000 -500 1 1000 0 3 108>
   V_SPACE <28 389 0>
   SIZE 280000
   "\n\tMany users mistype E-mail address"
  .STR
   "\n\tOften mailboxes are down or over-quota"
  .STR
   "\n\tThe bounce is the only way the user knows that something ba
 d happened"
END PICTURE
NOTES
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  BACKFILL <34 2 5 1000 0 0 0>
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   "Could interact badly with mailing lists and other people's whit
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   "\nStay out of heated discussions on related issues like SPF!"
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   "\n\tjoe-jobs annoy random third-parties, but false positives af
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 and viruses, and forward the cleaned mail to your servers"
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   "\nNo investment in hardware, software, ongoing management and m
 aintenance"
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