MailEnable standard 4.26 log : (taken with SmartSniff)
250-proweb.ca [220.127.116.116], this server offers 5 extensions
If one of theses command doesn't appear (ex. 250-) microsoft exchange servers will stop the process and send a "#5.5.0 smtp;500 Non RFC-compliant response received" bounce mail to the outlook client (the sender). I say ms-exchange but I succeed with some; but all the errors come from some of them.
But why did ME server could forget to write one command of the list ?
Because of the tech who try to hack ME registry to gives a feature (DSN "Delivery Status Notification Confirmations") to a demanding client. But with missing values in the HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Mail Enable\Mail Enable\Connectors\SMTP\Extensions\DSN registry key...
2 problem solved in 1 time !
Next time, when something "seems" to affect nothing, remove all traces anyway !