If you have a close look at Send Email's 3 exits, you'll note that they all output a structure called Delivery Status, which looks as follows:
As you can see this structure contains the raw smtp Message as well as 3 repetitive Address Status structures, which will contain one instance for each address specified in the message (the address will be in one of the 3 instances according to the results for that specific address).
If you're getting the "Email not sent" (rather than "Email was not sent"), then I deduce that the Send Email model exited through the Not Sent exit, and in that case, the Sent Addresses repetitive element is sure to be empty, and the address (or addresses) you specified will be in either the Invalid Addresses or the Unsent Addresses elements.
In order to figure out why the mail was not sent you must either model a process that analyzes this structure (which is what you should do anyway if you're modeling real-world send mail functionality, rather than a simple demo), or for a quick review, trace the send mail demo process as it is using the visual debugging feature.
Regarding the error message you get when you supply an smtp server, it would be helpful if you can send us details of the Tersus version you're using the detailed exception stack, which appears in [application root]/work/logs/tersus.log.
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