We have windows 2003 server that has to send an email to an Exchange 2007 server every time a user creates a purchase order through the server. It had been working fine but then we added a few 2008 domain controllers and now it can't find the Exchange server. Using smtpdiag I can see it is trying to send to a number of hosts on the LAN which aren’t email servers. I'm wondering how it has got these MX records because they are not in our DNS. Any help would be very much appreciated.

If it is sending emails to the severs which are in your domain, it will not look for the MX record for that. How ever if the servers are outside your domain, probably you can have a look into the Smart host settings in the SMTP connector on the E2K3 server.Raj

So the Windows 2003 server is sending via IIS SMTP? If its trying to send to your SMTP domain and there are no MX records defined in DNS, then its attempting to send to the A record of the domain.This is a requirement per RFC 5321:The lookup first attempts to locate an MX record associated with the name. If a CNAME record is found, the resulting name is processed as if it were the initial name. If a non-existent domain error is returned, this situation MUST be reported as an error. If a temporary error is returned, the message MUST be queued and retried later (see Section 4.5.4.1). If an empty list of MXs is returned, the address is treated as if it was associated with an implicit MX RR, with a preference of 0, pointing to that host. If MX records are present, but none of them are usable, or the implicit MX is unusable, this situation MUST be reported as an error.If one or more MX RRs are found for a given name, SMTP systems MUST NOT utilize any address RRs associated with that name unless they are located using the MX RRs; the "implicit MX" rule above applies only if there are no MX records present. If MX records are present, but none of them are usable, this situation MUST be reported as an error. When a domain name associated with an MX RR is looked up and the associated data field obtained, the data field of that response MUST contain a domain name. That domain name, when queried, MUST return at least one address record (e.g., A or AAAA RR) that gives the IP address of the SMTP server to which the message should be directed. Any other response, specifically including a value that will return a CNAME record when queried, lies outside the scope of this Standard. The prohibition on labels in the data that resolve to CNAMEs is discussed in more detail in RFC 2181, Section 10.3 [38].http://tools.ietf.org/html/rfc5321So, do you have a mx record defined and pointing to the Exchange Server? If not, create one. This will allow SMTP mailers outside of Exchange to send mail correctly.