Why wouldn't a "sent' email be received?

If you didn't get an email that they bounced, the most likely thing is that you mistyped the email address and they went to someone else. Or, they got there and went into the person's spam folder and they need to check there.

I don't know for sure what happens if someone has blocked your email. A few times, when replying to all of a group, I've gotten an email that a particular person won't accept email unless they already have your email address on a list of ones they will accept. But, that message is different from the one you get when the email address doesn't exist or something is wrong with it for another reason.

If the emails are in your sent box, chances are they did go out and the problem is something other than your email program not working right.

Hope you figure this out. Friends and I sometimes have that happen--an email seems to get lost in the ether, never to be seen again. But, this is very rare.