"Kevin D. Goodknecht Sr. [MVP]" wrote:

> Aaron (ireland) wrote:
> > Hi Kevin,
> >
> > It was advised that we use dhcp to provide dns settings such as the
> > external dns. I never understood why they had us provide client's
> > with external dns when we use a proxy server. Maybe the installation
> > of a new firewall etc.. will resolve this issue. Then I can remove
> > external dns. See some clients access pop3 mail from external
> > server's and without having external dns entries the clients are
> > unable to recieve mail.
>
> POP3 mail clients such as OE and Outlook will use the DNS in the client
> IPConfig for resolution unless it too is using a POP3 proxy, in which case
> the proxy resolves the POP3 server's name.
> If you use a Proxy, the web browser will get its DNS resolution from the
> Proxy server, the only sites that will use the DNS in the client's IPConfig
> are the sites that are configured to bypass the Proxy server.
>
> Have you tried nslookup against the internal DNS to resolve the POP3
> server's name?
Results;
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\username>nslookup mail.company.ie
*** Can't find server name for address 10.0.0.1: Non-existent domain
Server: dns1.cwm.dublin.isp.net
Address: xxx.xx.xxx.xxx

Non-authoritative answer:
Name: mail.compamy.ie
Address: xx.xxx.xxx.xxx <<Public IP


> If it can the problem is not DNS, if it cannot, is the a name conflict in
> your local DNS server?
> What I mean by a name conflict, is the POP3 server's domain name the same as
> your internal Active Directory domain name?

I presume that they are the same as they reside on the same box. I used
something like company.local for internal domain and company.ie for public
domain. To answer your question yes I think they both have the same name.

> If this is the case, there are several of ways to resolve this. First, use
> nslookup against the ISP's DNS to resolve your POP3 server's name, like this
> nslookup <mailserver'sFQDN.> <IPAddrOfISPDNS> (It is very important to add
> the dot after the mail servers' FQDN. to keep nslookup from appending the
> DNS suffix search list)
>
> If the mail server's name is an A record or a CNAME that points to an A
> record in your public domain, create an A record with the mail server's name
> and matching IP in the internal DNS.
>
> If the mail server's record is a CNAME that points to the ISP's mail
> server's name, create an identical CNAME in your internal DNS.
>
>
> > Maybe the problem is with ISA 2000 which is due to be upgraded. Any
> > comments would be great. Thank you.
>
> I tried ISA back when it first was released, I didn't understand about
> creating the proper rules, so I opted for a different proxy server that had
> default rules that worked out of the box. I just never tried ISA again.
>
> You are going to have severe network issues if you use the ISP DNS in TCP/IP
> on the client's NIC, all must use the internal DNS.
>
> --
> Best regards,
> Kevin D. Goodknecht Sr. [MVP]
> Hope This s
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