Problem
A Domino 5.0.3 or later server is configured to send SMTP messages outside the local Internet domain via a Sendmail relay server. A secondary Sendmail server is set up to provide failover in the event the primary relay is down. Creating a failover SMTP Connection document that references the secondary Sendmail host does not appear to work. When the primary relay host is unresponsive, the dynamic cost is set to "1," and the message is queued in MAIL.BOX, pending the next scheduled retry interval. This behavior was further tested using two SMTP Connection documents referencing the same Foreign SMTP Domain document with routing costs set appropriately.
One method used for failover is entering a Fully Qualified Host Name (FQHN) in the "Relay host for messages leaving the local internet domain" field (in the Configuration document's Routing/SMTP, and Basics tabs), and configuring DNS so that there are two IP addresses mapped to this FQHN.
Is there another way relay failover can be established?
Solution
This behavior was reported to Quality Engineering as SPR# SPRR4LRMN7; however, it was determined that Domino is working as designed.
Domino SMTP outbound failover utilizes MX records in DNS. In the environment described above, set the "SMTP MTA relay host" field in an SMTP Connection document's Basics tab to the FQHN of the relay server (such as SMTP.ACME.COM). Then create multiple MX records for this host in DNS, and manipulate their preferences in DNS to configure failover functionality.
http://www-1.ibm.com/support/docview.wss?uid=swg21095740