GWIA version 8.00.02

Trying to send mail to a domain:

This domain has some problems with its DNS. It has 7 MX records. The first three (priority wise) do not resolve. The last 4 are fine. See: MX Lookup

GWIA should be able to handle it, but instead we get bounces: "(550 Hostname/Domain name not valid or not available.)"

How do I troubleshoot?