Hello, when having multiple Edge Servers and having an MX record for each of them, if one of the Edge Server Fails and it has top priority, will the e-mails be directed to the next Edge Server in Priority or it will still forward the e-mails even though the server has problems. I am asking this because in some situations having a round robin dns will still forward requests even if one of the server is down.

Depends. See the Wikipedia article, which is good. Why not use MX records with the same preference? http://en.wikipedia.org/wiki/MX_recordMCTS: Messaging | MCSE: S+M

On Wed, 26 Jan 2011 20:17:48 +0000, acmsoft wrote: >when having multiple Edge Servers and having an MX record for each of them, if one of the Edge Server Fails and it has top priority, will the e-mails be directed to the next Edge Server in Priority or it will still forward the e-mails even though the server has problems. Which MX is chosen is a function of the sending SMTP client. If a MX is unvailable the client *should* use an alternate MX. >I am asking this because in some situations having a round robin dns will still forward requests even if one of the server is down. DNS doesn't forward anything. If you have multiple edge servers, is there a reason they don't have an equally weighted MX preference value? --- Rich Matheisen MCSE+I, Exchange MVP --- Rich Matheisen MCSE+I, Exchange MVP

Which MX is chosen is a function of the sending SMTP client. If a MX is unvailable the client *should* use an alternate MX. If the client becomes aware and uses the alternate MX then it is fine. Regarding the DNS, for an internal client which uses the internal mail CAS server name, if I create a round robin dns entry for the 2 CAS servers, if one of the CAS is not working what happens ?

It is not recommended to use DNS Round Robin. You'll have to take manual steps to detect issues and failover. Client DNS caches cause slow failover. This solution breaks affinity for some protocols such as Outlook Web App, Exchange Web Services, and Exchange Control Panel. Understanding Load Balancing in Exchange 2010 http://technet.microsoft.com/en-us/library/ff625247.aspxMCTS: Messaging | MCSE: S+M

Hi acmsoft, Jon-Alfred is right. it is not recommend to use DNS Round Robin. If you are using DNS Round Robin and one of the CAS is not working, the DNS Server will continue to send clients to that host because has no awareness that the server is down. Thanks, Evan Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.