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Open Relaying

For relay testing tools, see Testing Open Relays

What are open relays?

http://guide.vsnl.net.in/spam_busting/articles/open_relays/

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Filtering open relays

Open Relay DNS Blackhole Lists

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Testing Open Relays

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Tools

For relay testing tools, see Testing Open Relays

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Techniques

Discussion and the format for relay tests.

http://fightrelayspam.homestead.com/
http://www.chebucto.ns.ca/~af380/envelopes.txt
ftp://ftp.monkeys.com/pub/mail-tools/perl/mrt/test.patterns
http://arpa.org/erfm.pl (Pull relay IP addresses from a mail spool)
http://arpa.org/erfl.pl (Pull relay IP addresses from a sendmail log)
http://www.aupads.org/working.html
http://www.reedmedia.net/misc/mail/open-relay.html

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Known Testing Policies

http://mxdb.com/list/ (this site lists known relay testers)
http://basic.wirehub.nl/proxyscans.html
http://www.demon.net/helpdesk/announce/2002/da2002-07-26a.shtml
http://www.ja.net/CERT/JANET-CERT/mail/anti-spam/active.html

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Fixing Open Relays

How to prevent unauthorised third-party mail relaying through your servers.

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http://www.mail-abuse.org/tsi/ (MAPS Transport Security Initiative. Mirror: http://www.postfixgate.com/fix/)
http://www.ja.net/mail/anti-spam/relayfix.html (see also http://www.ja.net/mail/mailer_shield/)
http://www.chebucto.ns.ca/~af380/otherresources.html (Advice from the dead ORBS site)
http://www.ordb.org/fix/
http://www.ipa.go.jp/security/ciadr/antirelay.html (Japanese)
http://relays.osirusoft.com/mtafix/
http://www.declude.com/Hijack/ (hmm...)
http://www.mycert.org.my/mailabuse/antirelay.html
http://support.kivex.com/open_mail_relay_links.htm
http://pf.econ.kobe-u.ac.jp/mac/spam/anti-spam.html (Japanese)

Specific mail servers

Advice specific to a particular mail server.

http://www.exchangeadmin.com/Articles/Index.cfm?ArticleID=7696 (Microsoft Exchange)
http://www.slipstick.com/exs/relay.htm (MS Exchange)
http://support.microsoft.com/view/tn.asp?kb=319356 (Exchange 2000)
http://www2.tsc.com/~bobp/nms-no-relay.html (Netscape Messaging Server)
http://www.fwtk.org/fwtk/patches/patches.html#2.2 (SMAP)
http://docs.info.apple.com/article.html?artnum=106762 (Apple OS X)
http://www.postfix.org/basic.html#relaying (Postfix)
http://www.rince.de/block/ (Tobit)
http://support.ipswitch.com/kb/IM-19980116-JB02.htm (Ipswitch IMail)
http://www.deerfield.com/support/WinGate/kb/index.htm?a=1484 (MDaemon)
http://www.stalker.com/CommuniGatePro/AntiSpam.html#Relay (Communigate Pro)
http://www.exim.org/howto/relay.html (Exim)
http://www.isode.com/whitepapers/ic-8411.html (M-Switch)
http://www.vm.ibm.com/related/tcpip/spamming.html (IBM VM)
http://www.rockliffe.com/support/docs/html/1/00/10009.asp (Rockliffe Mailsite)
http://www.eudora.com/worldmail/questions.html#Heading58 (WorldMail)
http://razor.bindview.com/publish/advisories/adv_iis_smtp_null_relay.html (IIS SMTP)

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Sendmail

http://www.sendmail.org/tips/relaying.html
http://www.sendmail.org/antispam.html
http://www.sendmail.org/~ca/email/relayingdenied.html
http://sial.org/sendmail/

http://www.usenix.org/publications/library/proceedings/lisa97/22.harker.html

http://glennf.com/spam/sendmail.antispam.html
http://www.gtoal.com/spam/sendmail.html
http://www.rediris.es/mail/generador/ (Spanish)
http://www.plus.or.kr/document/etc/sendmail.html (Korean)
http://www.users.kudpc.kyoto-u.ac.jp/~w55062/spam.html (Japanese)

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Check_*

http://www.sendmail.org/~ca/email/chk-opt.html
http://www.sendmail.org/~ca/email/check.html
http://www.sendmail.org/~ca/email/chk-89.html
http://www.sendmail.org/~ca/email/chk-810.html
http://hexadecimal.uoregon.edu/antirelay/

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Non-English help

Short phrases to send to foreign relay administrators.

http://www.cybernothing.org/pub/abuse/relay/
http://www.chebucto.ns.ca/~af380/jpadmin.txt (Japanese)
http://www.nanet.co.jp/rlytest/index.html (Japanese)
http://www.stopchinaspam.com/ (Chinese)

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Other Anti-spam Relaying Measures

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See also: Preventing > User Control

Teergrubing or Honeypots

Fake open relays, which can slow down or block a spam-run.

http://www.iks-jena.de/mitarb/lutz/usenet/teergrube.en.html
http://fightrelayspam.homestead.com/
http://www.corpit.ru/cgi-bin/h0n5yp0t
http://www.palomine.net/qmail/tarpit.html
http://jackpot.uk.net/ (Java honeypot - works with Windows)
http://smtphoneypots.datalync.com/input/format-spec.html
http://www.benzedrine.cx/relaydb.html
http://www.openbsd.org/cgi-bin/man.cgi?query=spamd (OpenBSD)
http://www.martiansoftware.com/tarproxy/
http://www.angelfire.com/space/netcensus/gypsyshot.html

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Port 25 Blocking

ISPs prevent their users accessing any other PC other than their own mail servers on port 25.

http://www.byte.com/documents/s=126/BYT19990816S0017/
http://www.init7.net/anti-spam/

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Authorised Relaying

Authenticating that a user is really entitled to use a mail server.

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SMTP-Auth

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SMTP-Auth is a system to authenticate SMTP clients to servers.

Outline

http://www.faqs.org/rfcs/rfc2554.html
http://members.elysium.pl/brush/smtp-auth/server.html
http://beta.wsl.sinica.edu.tw/~ylchang/Email/sendmail-auth/ (Chinese)

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Servers

http://www.exim.org/exim-html-3.30/doc/html/spec_35.html (Exim)
http://www.sendmail.org/~ca/email/auth.html (Sendmail)
http://members.elysium.pl/brush/qmail-smtpd-auth/index.html (QMail)
http://www.cuni.cz/~vhor/qmail/smtpauth-en.html (QMail)
http://www.thecabal.org/~devin/postfix/smtp-auth.txt (Postfix)
http://postfix.state-of-mind.de/patrick.koetter/smtpauth/ (Postfix)

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Clients

http://members.elysium.pl/brush/smtp-auth/client.html
http://www.sendmail.org/~ca/email/other/auth-mua.html

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Pop-before-SMTP

http://spam.abuse.net/tools/smPbS.html
http://bsd.reedmedia.net/Software/Servers/SMTP_Mail/POP3_Authenticated_Relaying/
http://poprelay.sourceforge.net/ (Sendmail)
http://www.iecc.com/pop-before-smtp.html
http://mail.cc.umanitoba.ca/drac/index.html#solution
http://whoson.sourceforge.net/
http://alf.di.fct.unl.pt/AntiSpam/
http://mail.cc.umanitoba.ca/drac/index.html
http://kuerbis.org/smtpapop/ (Sendmail and Qpopper)
http://straylight.primelogic.com/popauthd/
http://www.koblenz-net.de/~horn/smtp_after_pop/doc/
http://www.davideous.com/smtp-poplock/ (QMail)
http://www.qmail.org/open-smtp3.tar.gz (QMail)
http://sapd.sourceforge.net/ (Sendmail)
http://www.lindstromconsulting.com/software.html (SodaPop)
http://www.stahl.bau.tu-bs.de/~hildeb/postfix/pop-before-smtp_en.shtml (Postfix)

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Extent of Open Relaying

Surveys of how prevalent open relays are.

http://www.imc.org/ube-relay.html
http://www.nta-monitor.com/news/spam-relay.htm (Survey of .UK)
http://www.angelfire.com/space/netcensus/smtp.html

See also: Stats > Blocking > Open Relays for statistics on numbers of open relays.

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To link to this page use: http://spamlinks.net/relay.htm

Last updated: 28 Agosto, 2019

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