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	<title>This Blog Is Not For Reading &#187; port blocking</title>
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		<title>Blocking port 25 considered harmful</title>
		<link>http://bob.jonkman.ca/blogs/2008/12/10/blocking-port-25-considered-harmful/</link>
		<comments>http://bob.jonkman.ca/blogs/2008/12/10/blocking-port-25-considered-harmful/#comments</comments>
		<pubDate>Wed, 10 Dec 2008 18:29:00 +0000</pubDate>
		<dc:creator>Bob</dc:creator>
				<category><![CDATA[considered harmful]]></category>
		<category><![CDATA[dnsbl]]></category>
		<category><![CDATA[dslreports]]></category>
		<category><![CDATA[port blocking]]></category>
		<category><![CDATA[smtp]]></category>
		<category><![CDATA[teksavvy]]></category>

		<guid isPermaLink="false">http://bob.jonkman.ca/blogs/2008/12/10/blocking-port-25-considered-harmful/</guid>
		<description><![CDATA[Blacklist services don't block e-mail, they merely provide an opinion of an IP’s reputation as a mail server.  Receiving mail servers are the ones that block e-mail, sometimes based on a poor opinion provided by a blacklist.]]></description>
			<content:encoded><![CDATA[<p><div id="attachment_618" class="wp-caption alignright" style="width: 310px"><a href="http://bob.jonkman.ca/blogs/?attachment_id=618"><img src="http://bob.jonkman.ca/blogs/files/2011/11/coffeine-abuse-300x200.jpg" alt="Coffee cup with a broken handle on a cluttered desk" title="Coffeine abuse" width="300" height="200" class="size-medium wp-image-618" /></a><p class="wp-caption-text">Coffeine abuse by maciekbor</p></div>Over in the <a title="TekSavvy forum - dslreports.com broadband community" href="http://www.dslreports.com/forum/teksavvy">Teksavvy Forum</a> at DSLReports <a title="DSLReport user R0cky" href="http://www.dslreports.com/profile/1206349">Rocky Gaudrault</a>, the owner of my ISP, <a title="Teksavvy Solutions Inc." href="http://teksavvy.com/">Teksavvy</a>, started a discussion on blocking port 25 entitled &#8220;<a title="DSLReports: Forums » O Canada! » Canadian » TekSavvy » Argg.... UCEPROTECT... very frustrating!" href="http://www.dslreports.com/forum/r21545801-Argg-UCEPROTECT-very-frustrating">Argg&#8230;. UCEPROTECT&#8230; very frustrating!</a>&#8220;.  This is <a title="Bob Jonkman's reply to R0cky: &quot;Argg.... UCEPROTECT... very frustrating!&quot;" href="http://www.dslreports.com/forum/r21558725-Re-Argg-UCEPROTECT-very-frustrating">my reply</a>:</p>
<blockquote><p>Two cents I&#8217;d like to contribute:
</p>
<p>
The <a title="UCEPROTECT®-Network - Germanys first Spam protection database" href="http://www.uceprotect.net/en/index.php">UCEPROTECT</a> service isn&#8217;t blocking e-mail, it merely provides an opinion on an IP&#8217;s reputation as a mail server. Technically, this opinion is expressed with a <a title="Wikipedia: Domain Name System Blocking List" href="http://en.wikipedia.org/wiki/DNSBL">DNSBL</a>.
</p>
<p>
When mail doesn&#8217;t get delivered, it&#8217;s the receiving mail server that blocks it, not UCEPROTECT. The recipient may reject the mail based on the opinion of the DNSBL, but if that DNSBL gives bogus information then the recipient will be blocking legitimate mail. The fault is with the mail recipient for choosing a poor DNSBL. It&#8217;s not Teksavvy customers who can&#8217;t send e-mail, it&#8217;s the recipients who are refusing to accept it.
</p>
<p>
Even if Teksavvy did block port 25, there&#8217;s no guarantee that poor DNSBL services would whitelist Teksavvy&#8217;s servers. DNSBLs are run at the whim of their operators, and they can blacklist anything they like. The people who use these services need to understand that they&#8217;re letting someone else decide what mail they can receive, completely out of their control.
</p>
<p>
Port blocking is ineffective as a spam fighting technique &#8212; ISPs started port blocking in 2001, but if port blocking is so good, why is there still spam? Most spam still comes from disreputable bulk mailers running large-scale operations. Remember the <a title="Google News: McColo" href="http://www.google.ca/news?q=mccolo">McColo servers</a> from a few weeks ago? When that one operation was shut down there were reports that spam volumes dropped by 30%. To fight spam, concentrate on the large-scale spammers.
</p>
<p>
There are lots of spambots running on poorly protected home computers, but that&#8217;s a symptom of poor security. Blocking port 25 won&#8217;t fix the security problem. To fight poor security it&#8217;s far better to identify the compromised computers, and provide them with tech support to fix the problem. Teksavvy is in a better position to do that than any other service provider I know.
</p>
<p>
There is no benefit to Teksavvy customers in blocking port 25 &#8212; It doesn&#8217;t protect Teksavvy customers from spam. It might protect other ISP&#8217;s customers from Teksavvy spammers, but it also denies Teksavvy customers full access to the Internet. Full, unblocked access is one of the main differentiators that Teksavvy brings to the market. Don&#8217;t give that up, Rocky.
</p>
<p>
Blocking ports also prevents legitimate services. <a title="RFC2821 - Simple Mail Transfer Protocol - Section 2.2 The Extension Model" href="http://tools.ietf.org/html/rfc2821#section-2.2">ESMTP</a> extensions like <a title="RFC3464 - An Extensible Message Format for Delivery Status Notifications" href="http://tools.ietf.org/html/rfc3464">DSN</a> rely on a direct connection to transfer Delivery Status Notifications. If a relay server doesn&#8217;t implement DSN then status notifications don&#8217;t get through. If port blocking is turned on, the smart host providing the relay service had better implement every ESMTP extension that exists. And that could still block other services that rely on unfettered access to port 25 (<a title=" RFC 2447 - iCalendar Message-Based Interoperability Protocol (iMIP)" href="http://tools.ietf.org/html/rfc2447">iMIP</a> anyone?)
</p>
<p>
Blocking one port today is the thin edge of the wedge to blocking other services. Already I&#8217;ve seen requests for blocking ports 137 and other Netbios ports. If Teksavvy starts port blocking then every time there&#8217;s a new vulnerability the Teksavvy execs will need to agonize over whether to block or not. DNS is broken? Block port 53. There&#8217;s child porn on Usenet? Block port 119. <abbr title="Canadian Recording Industry Association">CRIA</abbr> threatens to shut down encrypted filesharing? Block port 443. If Teksavvy has a policy of no port blocking, all these decisions are moot.
</p>
<p>
I left Rogers because of port blocking, and came to Teksavvy because of unfettered access. Please don&#8217;t take that away.
</p>
<p>
&#8211;Bob.</p>
</blockquote>
<hr />
<p style="font-size:smaller"><a href="https://secure.flickr.com/photos/maciekbor/2403213825/" title="Coffeine abuse | Flickr - Photo Sharing!">Coffeine Abuse</a> by <a href="https://secure.flickr.com/people/maciekbor/" title="Flickr: maciekbor">maciekbor</a> is used under a <a href="https://creativecommons.org/licenses/by/2.0/deed.en" title="Creative Commons — Attribution 2.0 Generic — CC BY 2.0:"><img src="https://i.creativecommons.org/l/by/3.0/88x31.png" alt="CC-BY" width="88" height="31" style="float:left;" />Creative Commons Attribution</a> license.</p>
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