Postfix sending emails via multiple broadband lines

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http://serverfault.com – I have a site that send out emails from a postfix server. They have multiple broadband lines for load balancing and failover. I want them to be able to send out emails though both lines without the risk of being blocked as spam. Both lines have a static address and have a PTR record on them which also have a records that resolve to the IP addresses server.domain.com server2.domain.com in the main.cf myhostname = server.domain.com SPF records are also being configured as well my main question is: should the first line on server.domain.com go down would there be a risk of the emails being (HowTos)