Load Balance Outgoing Email

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How can I load balance outbound email?

1. Configure N relay hosts host1, host2, ..., hostN.
2. Using either a load balancer or a DNS which can do round-robin handling, make the DNS A record mail.whatever.com resolve to the IP addresses for host1, host2, ..., hostN.
3. Tell your users to configure their SMTP clients to use mail.whatever.com as their outbound mail relay.

When users try to send mail, their mail clients query the DNS for mail.whatever.com, get the list of IPs, and then try the first IP from the list. If the DNS shuffles the list (round-robin or other metohd), then the load should be spread out between your N relays.