Multiple mail server support
You can configure multiple mail servers for a Email Engine installation. For each configured mail server, you can specify a failover mail server. If the mail server being used stops working, the Email Engine switches to the available failover mail server and continues processing mails. The following figure depicts this functionality.
Multiple mail servers configured for failover
(Click the image to expand it.)
In the illustration, M1 is specified as the primary mail server, and M2 and M3 are specified as failover servers. If the Email Engine detects that M1 is not working, it checks whether M2 is available, and if so, it switches to M2.
The Email Engine then tries to connect to M1, and if that is not yet working, it connects to M2. Then, if the Email Engine detects that M2 is not working, it checks for the availability of M1. If M1 is still not working, it looks for the failover server for M2, which is M3. If M3 is available, it switches to M3 and continues processing messages as described in the preceding note.
If none of the configured mail servers is working, the Email Engine produces an error and stops processing.
When switching from a server being currently used to its failover server, an entry is added to the stderr.log (Windows) or emaild.sh_log (UNIX) file. However, when switching back from the failover server to the primary server, no change is made to stderr.log or emaild.sh_log.
The multiple mail server support is currently available for the SMTP protocol only.