Next I'd suggest that you use the Message Tracking Center in Exchange Server to see what's happening with the message in question. It could be sitting in a queue somewhere.
I'd also suggest you confirm that the banner returned on your telnet session identifies the telnet server you're connecting to as an Exchange 5.5 server and not some other Windows telnet service. Depending on what you have installed on this server I've seen numerous situations like yours in which a "rogue" telnet service (or more properly one doing its job that the telnetting administrator has completely forgotten about!) exists and is accepting messages, only to queue them up since it's unaware of Exchange Server. Make sure you're really connecting to the right telnet session on port 25 or whatever alternate SMTP port you may have configured.
Finally, I'd confirm that all the Microsoft Exchange services are up and running on that server and that you're not getting any errors or warnings in the application event log on the Exchange server.
If after working through all this you're still having an issue, ping back in to SearchExchange.com and we'll try to assist further.
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