Messages from friends

I've been telling some friends about nabaztag, and they've sent my nabaztag a few emails, which have worked, with nabaztag reading out the subject line.

However, everytime they try and send one now, they get a message back, saying email failed, as you must send a message from the account that the nabaztag was setup from.

Why did this work the first few times that they sent an email from their own account ?

Secondly, is there anyway for someone to send a message to my nabaztag, that will be read out, without them having to buy their own nazzie. It seems silly they can't simply send a few messages to my nazzie, as thats what its partly designed for i.e receiving and relaying messages