$emailed = array('email@example.com', 'firstname.lastname@example.org');
$message = count($emailed) > 10
? implode(array_slice($emailed, 0, 10), ', ') . 'and ' . count($emailed) . ' others were sent an invite!'
: implode($emailed, ', ') .
count($emailed) == 1 ? ' was sent an invite' : ' were sent invites!';
echo(implode($emailed, ', '));