Your program used port 25 but now you're telnetting port 587... could that be the problem?

Edit (in response below):

$Message->send_by_smtp('localhost:587');   #-- assuming program runs o
+n same host as mailserver
                                           #   (otherwise also adapt '
+localhost' or try to  
                                           #    set it to '127.0.0.1' 
+in case of IP6 confusion)
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