Backup SMTP not working

First of all thank you so very much for this module. I've used it on many sites.

One problem that I have encountered in the 6x branch is that I've never been able to get the backup SMTP to work. Upon failure of the primary SMTP there is never an attempt to the secondary. I currently have a client that shuts down their main mail server for various reasons over the weekend. They have a backup mx server to process their incoming mail when the main is down and they have a mailhop server for outgoing when the main is down. It's an e-commerce site and they cannot afford to have email's go to email heaven when their main mail server goes down.

Both servers are configured identically so that the same username, password, ssl, port etc are the same. For example I can flip-flop the main SMTP with the Backup SMTP and email still gets processed appropriately. The problem is that when the main server is down I just get a generic failure report and that's it. Like I said, there's never an attempt to the backup SMTP server.

Any help would be greatly appreciated. Thanks