If the e-mail didn’t get through then you should have get a delivery failure notice from the mailserver, in which you should see what caused the failure. (E.g the recipient’s mailbox is full (in this case the recipient’s server will send the mail), or the email address is not correct (in this case your mailserver will answer.) But definitely you have to get an email about it.
If you don’t receive any response, then the recipient doesn’t answer your email.
I hope this helps.