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Symptom
Outbound messages are bounced with one of the following errors:
"550 MX record points to an invalid IP for domain:<domain> - psmtp"
"550 Neither MX nor MTA found for domain:<domain> - psmtp"
"550 No MX and invalid A record for domain:<domain> - psmtp"
"550 Host not found for domain:<domain> - psmtp"
Resolution
These errors are returned when the outbound message appears to be an invalid message being sent to a nonexistent domain, a domain with no mail servers, or a domain with MX records intentionally designed by spammers to appear to be legitimate.
Below is a detailed description of the state that causes each error:
"550 MX record points to an invalid IP for domain:<domain> - psmtp"
This error is returned when the MX record lookup succeeded but returned an invalid reference such as no IP address or an IP address such as 0.0.0.0 or 127.0.0.1 (localhost/loopback).
"550 Neither MX nor MTA found for domain:<domain> - psmtp"
This error is returned when the MX record lookup returned no MX records and Postini was able to resolve the domain to an A record, but the attempt to connect to the IP address in the A record failed.
"550 No MX and invalid A record for domain:<domain> - psmtp"
This error is returned when the MX record lookup returned no MX records and Postini was able to resolve the domain to an A record, but the IP address listed in the A record is invalid, such as 0.0.0.0 or 127.0.0.1 (localhost/loopback).
"550 Host not found for domain:<domain> - psmtp"
This error is returned when the MX record lookup returned no MX records and Postini was attempted to resolve the domain to an A record, but that attempt failed as well.
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