Paul.Murphy at argentadiscovery.com
Wed Nov 25 16:50:19 EST 2009
Dave O'Neill wrote:
> However, if you split your MXes on different networks (different colo
> facilities, for example) you have no way of knowing if the sender can
> actually route to your primary. It's entirely possible that due to
> network outages or weird peering issues they may have no route to the
> primary, or have their connection to it is so slow that it times out.
> Both will cause their legit mail to be retried on the secondary, which
> might be reachable given that it's on a different network.
However, our circumstances are fairly unusual, in that we have multiple sites, all connected to the same ISP's backbone, and with DSL backup connections which route between the sites entirely differently from the main connections.
As a result, it is highly unlikely that routing issues or an outage will make one server accessible and the other not, and our connection uptime is 100% for the last 2 years.
I've also considered using data on when a message was last received via a server and what its current load is as the criteria for deciding whether the primary is up - we already log everything in a database, so checking how long ago the primary successfully delivered a message into the company, and whether it is capable of accepting new connections, is fairly simple for us.
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