The Send and Receive Connector names for Exchange 2007 / 2010 do not have to match. Telnet will only ever show you the Receive Connector name, it cannot show the Send Connector. It's part of why it's important to identify the mail system in question :)
Which makes the answer to this:
> Is telnetting internally to mail.domain.com a valid banner test?
No for Exchange 2007 and 2010, and yes for Exchange 2000 and 2003.
The only place you're going to see your banner is in message headers, or if you manage to get another mail server up and running, so you can send test messages to it.
The general standpoint for anti-spam systems is that they must look at all PTR records for a given IP and accept the mail if any match. Of course, you cannot be sure everyone will obey that so it can make a great deal of sense to simplify things if possible.
Do you actually suffer because of this? It is entirely possible that MXToolBox simply do not account for multiple PTR records for a single host.
I guess you've tested public name resolution of your PTR record separately?
Chris
