The Devil Is In The Details …
 

And this is going to be a quick post about one of those “details” … let’s say your running two servers in a cluster and the 2nd server catches on fire (not that mine did).
 

If half of your users are on Server A and the other half are on Server B … what will happen to the mail being delivered to the users on Server B when it goes out in a ball of flames?
 

Logic dictates that, since you are running in a cluster, the mail router will “see” the 2nd server as being down and deliver the emails to the Server A mail file of those users … right?
 

Well, you’re correct *only* if you have configured the router to do that.
 

How To Configure The Router To Deliver Emails to Cluster Mates …
 

If you ever run into this same situation (as I did), you need to do the following:
 

(a) Open your Domino Directory

(b) Go to the “Configurations → Server → Configurations” view.

(c) Open your Server A configuration document.

(d) Put the Server A configuration document in Edit mode.

(e) Go to the “Router → Advanced → Control” tab.

(f) Make sure that “Cluster failover” is set to “Enabled for all transfers in this domain”.

(g) Save the server configuration document.

(h) Repeat for all your other server configuration documents.
 

 
Once you’ve made the change, make sure to replicate your Domino Directory around and issue a RESTART TASK ROUTER on them all.
 

Conclusion …
 

Domino Clusters are awesome and they just work out of the box … but that’s one of the details that you need to be aware of if you want mail to flow even when one of your clustered server is down.
 

Thanks for reading!
 

Marc