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<TITLE>RE: DNS Cache and Sendmail Msg-Id</TITLE>
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<P><FONT SIZE=2>Sorry, now that I look at it a little closer, I'm thinking of the ESMTP id as listed in the received headers.</FONT>
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<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: mikea [<A HREF="mailto:mikea@mikea.ath.cx">mailto:mikea@mikea.ath.cx</A>]</FONT>
<BR><FONT SIZE=2>Sent: Tuesday, May 20, 2003 1:58 PM</FONT>
<BR><FONT SIZE=2>To: MAILSCANNER@jiscmail.ac.uk</FONT>
<BR><FONT SIZE=2>Subject: Re: DNS Cache and Sendmail Msg-Id</FONT>
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<P><FONT SIZE=2>On Tue, May 20, 2003 at 01:31:25PM -0400, Derek Winkler wrote:</FONT>
<BR><FONT SIZE=2>></FONT>
<BR><FONT SIZE=2>> Couple of kinda off topic questions...</FONT>
<BR><FONT SIZE=2>></FONT>
<BR><FONT SIZE=2>> Is setting up a caching DNS server for the MailScanner machine a good idea?</FONT>
<BR><FONT SIZE=2>> Not sure how this would effect RBL lookups.</FONT>
<BR><FONT SIZE=2>></FONT>
<BR><FONT SIZE=2>> How unique is the sendmail message id, is it unique for that day or until</FONT>
<BR><FONT SIZE=2>> the process ids rollover or some other method used? Searched the internet</FONT>
<BR><FONT SIZE=2>> for this but couldn't find anything.</FONT>
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<P><FONT SIZE=2>Done properly, the caching DNS server will retain records for their</FONT>
<BR><FONT SIZE=2>TTL, so that you won't have to go all the way to DNSbl server each</FONT>
<BR><FONT SIZE=2>time you look up, e.g., flowgo.com. Unless, that is, I'm much</FONT>
<BR><FONT SIZE=2>mistaken.</FONT>
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<P><FONT SIZE=2>The sendmail message ID is intended to uniquely identify the message</FONT>
<BR><FONT SIZE=2>in the universe of all possible messages sent by all sendmail MTAs.</FONT>
<BR><FONT SIZE=2>It may even succeed at that. Certainly the date and time, sendmail</FONT>
<BR><FONT SIZE=2>process ID, and so on, are encoded in the 8.12 Message-ID -- down to</FONT>
<BR><FONT SIZE=2>a very small quantum of time. IIRC, earlier sendmails used a similar</FONT>
<BR><FONT SIZE=2>method, but the quantum was larger. Again, that's the way I understand</FONT>
<BR><FONT SIZE=2>it, but ICBW.</FONT>
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<P><FONT SIZE=2>Here's a randomly-chosen Message-ID from my system:</FONT>
<BR><FONT SIZE=2>Message-Id: <200305201731.h4KHVapE058947@mikea.ath.cx></FONT>
<BR><FONT SIZE=2> <date-->time moretime<pid-> machinename</FONT>
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<P><FONT SIZE=2>--</FONT>
<BR><FONT SIZE=2>Mike Andrews</FONT>
<BR><FONT SIZE=2>mikea@mikea.ath.cx</FONT>
<BR><FONT SIZE=2>Tired old sysadmin since 1964</FONT>
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