Sendmail problems - are they to do with DNS or not?

[Sami Yousif]

Anthony Seddon wrote:

> Hi,
>
> I am running sendmail 8.9.3 on a Linux box and the mailserver is connected
> to the internet via an ISDN router, which dials up as and when needed.
> Client PCs in the office use the linux box for internal and internet email.
>
> Our domain is byzak.co.uk and we can normally send 'internal' emails without
> any problems.  However, if for some reason the ISDN connection is down, then
> all emails including emails to our domain are queued / deferred.  I
> understand that this would be the case for emails outside our domain, but
> shouldn't emails to the byzak.co.uk domain go regardless?
>
> We are using Windows 95/98 clients running MS Outlook Express 4.  Outlook
> Express doesn't complain when sending the mail, however it takes about 60
> seconds to send the mail (a small text message).
>
> Do I need to install BIND on the Linux box and set up an MX record pointing
> to itself?

Yes. You should have a local dns server on the "near" side of the link. see
below...

>
> Am I right in thinking that sendmail does a DNS lookup on the sender?  If
> that is the case, then can I disable it as by the nature of our dial on
> demand connection, only people 'within the office' and within the domain can
> use our server to send mail.

Yes. sendmail does a DNS lookup. It can be disabled.. but you really shouldnt..

Check the /etc/resolv.conf on your mail server. It should only point to dns
servers that are either secondary or primary for your zone which are on the
"near" side of the ISDN link.

Your local dns server (you DO have a local dns server on the near side of the
link?) may need to be configured as a "stealth secondary" if your zones are
normally held elsewhere (on the far side of the ISDN link)

The win95/98 clients also need to have their dns server set for the machines on
the "near" side of the link

This btw should decrease the load on your ISDN link and improve performance...
(as would a correctly configured squid proxy server on the near side of the
link.... but i digress....)



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Sami Yousif

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