OT: Load Balancing & redundancy using Multiple A records

Richard Frovarp Richard.Frovarp at sendit.nodak.edu
Fri Nov 23 16:25:12 GMT 2007

ram wrote:
> We use multiple MX records for our MailServers for all our clients. 
> We have already added one data center and had to inform all customers to
> add more MX records 
> Can I avoid changing of MX records by adding the new ips as multiple A
> records and using DNS round robin
> What are the problems associated with this kind of setup 
> Thanks
> Ram

SMTP is designed to handle failure across multiple MX records. If your 
round robin returns a box that isn't available (due to load or 
maintenance) or if the box is no longer in your round robin, but hasn't 
expired out of the remote DNS you'll have issues. The outgoing SMTP will 
try to connect to a MX that isn't available and will have no option for 
fail over. You would probably want to still have multiple MX records for 
this reason. If no MXs are available at delivery time it might result in 
a permanent failure, depending on the sending SMTP. You could have 
multiple A's for each MX so that you would still have failure.


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