Well, although no one can say with certainty the interest level of this guy, based on what you've said, first



"I think me and my mailman like each other. It's clear that we enjoy talking to each other. "

based on that line alone, Idk if it's true that he likes you but clearly you've established some rapport and have had conversations on more than one occasion. So that alone says there is some interest. Whether its that he "likes" likes you or is just enjoying talk... would be hard to say based on that alone but

the fact that when he reached your apartment, he actually engaged you again, kind of says a bit more to me. After you walked away he made an effort to engage you again even if it were just a comment like that he was finished with the day - I think really it was an invitation to conversation again, at the very least. Not only did he engage you again, but he alluded to the idea that his day was ending, possibly implying he has time now... Idk

as for your clumsiness in conversation, I totally understand this and I don't think you're alone in that those silent "10 year" moments are awkward. I know how this goes but I really think a lot of people experience this and you shouldn't be too hard on yourself. It's about feeling like you need to perform well for this person of obvious interest and attraction to us. we want to impress and attract them too and tend to think too hard on what to say and do. Layer that with the type of person who may be socially awkward anyway (me) and it's a killer situation... in a bad way lol. Don't be too hard on yourself because likely if there is mutual attraction, there's likely mutual awkwardness too and he may feel a bit the same too!

I agree with the one to say to keep to your doorstep and/or mailbox, what not.. see where it goes.