Why does the e-mail work when it's not connected?

Okay, so I have a new friend, YAY! But anyway, we traded e-mails recently and when I was bored and fooling around on my iPod, I entered in her e-mail to see what would happen. I expected it to turn red after a moment of watching the loading wheel by it, but to my surprise, it turned blue. So it was connected, right? I typed in hi, sent it, and waited. The read receipt came up a few moments later, but there was no reply. I sent a few other things and only saw that they were read, but there was never a reply from them. I showed my friend and she was confused because she's not connected to any Apple devices (that she knows of) nor does she have an iTunes account. It couldn't be that it's a family e-mail because the e-mail is literally her (very unique) name. Could it be a hacker?

She's not the only friend of mine who doesn't have any Apple related things attached to their e-mail. I tried checking with their e-mails to see if the same thing happens, and, well, some worked and some didn't. Though particularly interesting was that one e-mail turned red after loading, which I expected, but the send button never greyed out and I was able to send a hi to it. After that, the e-mail appeared to be connected to Apple or at least, iMessage. I don't get it. Are my friends just pulling some very coordinated "Oh, let's pretend we don't have Apple devices" trick on me, or are there idiot hackers using other people's e-mails for iMessage? I don't get it. Nothing harmful has happened, but it's confusing me why this is so…