Preventing MX record fallback

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http://serverfault.com – I have a website, example.com, running on a Windows 2008 server with IIS 7 and the "IIS 6" SMTP service. The website regularly sends out emails to [email protected] In rare instances, the MX record lookup for example.com fails, and so the SMTP service falls back to the A record, which I understand is expected behavior. However, this is not desired behavior, since the mail server for example.com is on a different machine, so the occasional email bounces. What's the best way to prevent this? EDIT: My DNS setup looks like this: A - example.com -> A - mail.example.com -> (HowTos)