@bigeno: yep, that is my suspicion as well
@marcov: yes, irrelevant:
Irrelevant if it was a reply to your post, which it wasn't.
I tried to only take input from the OP, not your assumptions about what he wants. At least not till he confirms them..
I'm trying to get some information in the thread so that the next OP feedback will narrow it down to what he wants. Not to pin him on something you think it is his purpose based on minimal info.
What benefits with regard to SENDING mail would the OP have in scenarion 2 versus scenario 1?
(I can actually imagine scenarios where the receiving mailserver checks if the sender is a mailserver)
Why can't he simply use Indy? There are IMHO too much open questions to narrow all answers down so much already.
Aside:
If you don't follow scenario 2 but say install your own mail server you would need root permissions anyway to listen on port 25 as you rightly indicate...
Or at least setuid. But that also complicates delivery. The integrated mailserver is still one binary delivery.