DNS Cache and Sendmail Msg-Id

Mike Kercher mike at CAMAROSS.NET
Tue May 20 19:08:19 IST 2003

I think you are correct about the DNS.  I always run a caching nameserver on my
mailservers to speed outbound delivery as well.

On the sendmail message ID's, I took a quick glance at my maillog:

May 20 13:04:21 genesis sendmail[32426]: h4KI4B532384: to=<user at domain.com>,
delay=00:00:09, xdelay=00:00:00, mailer=local, pri=122191, dsn=2.0.0, stat=Sent
May 20 13:04:24 genesis sendmail[32385]: h4KI4C532385: SYSERR: putoutmsg
(lsanca2-ar31-4-33-244-109.lsanca2.dsl-verizon.net): error on output channel
sending "550 5.7.1 Access denied": Broken pipe
May 20 13:04:24 genesis sendmail[32385]: NOQUEUE:
lsanca2-ar31-4-33-244-109.lsanca2.dsl-verizon.net [] did not issue
MAIL/EXPN/VRFY/ETRN during connection to MTA
May 20 13:04:36 genesis sendmail[32432]: h4KI4V532432: ruleset=check_relay,
arg1=[], arg2=, relay=[], reject=553 5.3.0
Rejected - see http://relays.osirusoft.com/

The message ID's seem to follow some sort of naming convention unique to each
server.  Your message ID's for the same timeframe (CDT) should reflect something
completely different, but also somewhat sequential.  I don't know exactly how
these ID's are generated, but they do change from day to day.


> -----Original Message-----
> From: MailScanner mailing list 
> [mailto:MAILSCANNER at JISCMAIL.AC.UK] On Behalf Of mikea
> Sent: Tuesday, May 20, 2003 12:58 PM
> Subject: Re: DNS Cache and Sendmail Msg-Id
> On Tue, May 20, 2003 at 01:31:25PM -0400, Derek Winkler wrote:
> >
> > Couple of kinda off topic questions...
> >
> > Is setting up a caching DNS server for the MailScanner 
> machine a good 
> > idea? Not sure how this would effect RBL lookups.
> >
> > How unique is the sendmail message id, is it unique for that day or 
> > until the process ids rollover or some other method used? 
> Searched the 
> > internet for this but couldn't find anything.
> Done properly, the caching DNS server will retain records for 
> their TTL, so that you won't have to go all the way to DNSbl 
> server each time you look up, e.g., flowgo.com. Unless, that 
> is, I'm much mistaken.
> The sendmail message ID is intended to uniquely identify the 
> message in the universe of all possible messages sent by all 
> sendmail MTAs. It may even succeed at that. Certainly the 
> date and time, sendmail process ID, and so on, are encoded in 
> the 8.12 Message-ID -- down to a very small quantum of time. 
> IIRC, earlier sendmails used a similar method, but the 
> quantum was larger. Again, that's the way I understand it, but ICBW.
> Here's a randomly-chosen Message-ID from my system:
> Message-Id: <200305201731.h4KHVapE058947 at mikea.ath.cx>
>              <date-->time moretime<pid-> machinename
> --
> Mike Andrews
> mikea at mikea.ath.cx
> Tired old sysadmin since 1964

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