In your domain's DNS configuration, you should have an SPF (Sender Policy Framework) record. This is not strictly required, but it is an essential step in reducing the likelihood that mail you is blocked as spam.
You should add the following to your SPF record, which authorizes Webvanta's email servers as senders of email that has a reply address with your domain name:
This is the IP address of the server that sends mail on behalf of the Webvanta system.
For more on optimizing deliverability of email generated by your site, see Configuring Reply-To Addresses and Optimizing Mail Delivery.