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skantechtech -> RE: Exchange 2003 SMTP DNS NDR Relaying Denied 5.7.1 (13.Sep.2004 11:34:00 PM)
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My last resolution did not fix the issue. I worked with Microsoft and now it appears to be fixed.
1 - Microsoft Exchange - SMTP Virtual Servers - Properties Remove all IP addresses. Let TCP/IP do the work.
2 - I set up TCP/IP on the mail server to look at my local servers.
3 - I went into my DNS Servers in the DNS snap-in. Forwarders tab. One of the DNS servers I had listed was no longer operational. Called my ISP, got new primary and secondary DNS IP addresses, they were apparently weeding out old servers and setting new ones up. Also per MS added 198.6.100.218 as a DNS server to my forwarder list.
On the DNS and Mail servers ipconfig /flushdns ipconfig /registerdns restart net logon service
Everthing appears to be running smooth, no one received an invalid NDR today. Will continue to monitor.
Here is a cut and paste from my ticket with MS>
When Exchange 2000 sends e-mail to the Internet using DNS to resolve external domain names a DNS query is done for the remote domain's MX records. In the event that the initial MX query returns a "server failure", Exchange 2000 will fall back to a DNS A record query. If this query is successful and there is an A record for the domain in question that happens to be listening on port 25, Exchange will make a connection to that server. However, if this server does not relay e-mail for the intended domain a NDR will be generated with a 5.7.1, or 5.5.0 error message.
There are several domains that have A records that point to IP addresses that accept connections on port 25, but do not relay for the same name space:
Mindspring.com is one example.
Resolution - - - - -
Resolve the DNS resolution problems that are causing occasional MX record failures.
Examples:
1. Internal DNS servers use forwarders to resolve external DNS queries and one of the DNS servers in the list returns "server failure" when doing DNS queries. Action: remove this DNS server from the forwarders tab.
2. The Exchange server has multiple default gateways set on a multi-homed server. This is not a recommended configuration and can cause a number of unexpected network problems. If the internal DNS server the internal NIC points to cannot resolve external DNS queries, this problem can occur. Action: remove the default gateway from one of the NICs.
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