We've added a new mail service mode called "SMTP Redirection (Lookup Record)". I's similar to the existing redirection service, however it adds the ability to redirect to multiple destination servers using using a DNS lookup record. Through this lookup record, you can define round-robin DNS (multiple A/CNAME records), equal priority MX records, or primary/secondary delivery (MX records). Examples are available in the documentation. This feature is available immediately at no extra cost.
For more information, see the update mail documentation: