Messaging Gateway

We are having problem with sending e-mail to a domin with Symantec Message Gateway 10.5.2.

This customer who have multiple MX records with different priority. They are correctly resolved from SMG as matched with mxtoolbox. The host for first two MX records are not reachable and the other two remaining is fine. However, our mail is stuck in mail queue and having the following error.

451 4.4.1 [internal] No valid hosts (unable to make any connections)

I believe SMG will try sending mail in queue to lower priority MX records if the high priority ones are not reachable. But I cannot confirm this by looking at audit report. Is that anyway to check or making sure SMG has really tried to send mail to lower priority MX records?

Thanks in advance.

When you are looking at the Message Audit log, click the plus sign next to Delivery. This will show you the IP addresses we have attempted delivery to.

Thanks for advice.

I already tried that before. It only shows IP address of sucessful delviery recipient. The mail stuck in queue has no such info and I'm not sure which IP address SMG is contacting. Just by looking to the error, I suspect it havn't try to contact IP address at lower priority MX record but I cannot verify that.