I've been having some email delays and in some instances undeliverable email over the last several weeks. My problem has been on both in-bound and out-bound delivery. I've done the same test on the actual internal email server with no delays.

Make sure your RF850 is running firmware 3.31 or newer. If you are running 3.31, you can try increasing the SMTP connections allowed in the RouteFinder. Here are two commands to increase the connections:

/etc/multiconf/scripts/flashqmailconfig SMTP_INCOMING 10
/etc/multiconf/scripts/flashqmailconfig SMTP_OUTGOING 10

This will increase the # of connections from 5 to 10

Here is a link to the latest firmware: