To be sure, the way to add multiple recipients to an e-mail on one line is as so:

johnny.doe@gmeal.com; (<- After pressing that it jumps down one line, no need for pressing "space")
mila.denila@hotmeel.com;
sonny.jim@abc.nut
etc.

You're doing this, right? I'm sending mails quite regularly to around 10 people and no hassle. Just takes a little longer for it to confirm that all mail's been sent, but they all receive the mail.