This may be a very basic question to ask, but I will ask it none the less. I have a Win2003R2 server running the smtp service native with IIS. It relays mail between the public and our internal mail server (not Exchange). Im finding that some of the outbound messages are not being delivered because the smtp service is connecting to the wrong mail server. For example, a message was sent out to a domain once and the ip address which was contacted resolved to the www.domain.com address. This address was not listed anywhere when I manually performed an nslookup of the domains mx records. I am seeing a few log entries where the error message is "relaying denied from [my public ip] You must authenticate first...." I understand the error message and why I am receiving it. What I dont understand is why the smtp service is not contacting the primary (or secondary) mail server based on the mx record listings?? Can any one shed some light or educate me as to why? Thank you

I don't know much about DNS or mail issues but perhaps your DNS entries might need some tweaking. When an MX lookup is made against your entries, the MX record with the least preference number is tried first. In other words, the smallest number is the highest priority. Double check your smtp and DNS configuration. Perhaps the experts have a better idea? :) jav

Correct. However for one.. Its not MY mx record. And two.. When looking at the intended recipients mx record (from my local dns server or a forwarding dns server) the ip address my smtp server is talking to is NOT listed in any mx records let along in a priority order. Guess I am really confused at how the smtp server has decided to try that particular server to attempt a mail exchange with?!

In regards to DNS, your SMTP server will look for hte domain's MX record as you would expect. The only exception that I know of for SMTP (and I am not a messaging expert) if if you configure your server to use a "smart host" rather than DNS to deliver mail. Unless the MX record for the target domain has recently changed and your server is using cached information, it should be using the listing of MX records returned from its DNS query.Visit my blog: anITKB.com, an IT Knowledge Base.