Failure Notices from one Sender Only

[merlin96]

I have been receiving Failure Notices from one friend who lives in Australia.  This was happening back in December and it got so bad we started using an alternative email address for a while and then it stopped.  Now it's starting again and almost all of her emails to me are bouncing back to her.  I'm not sure where to start in trying to figure out why it's happening and I have a feeling if I call tech support they are going to ask me if I received her most recent email.  I will say yes -- the one forwarding the most recent failure notice -- and they will say it was just a temporary problem and it's now fixed.  But it keeps happening and I'd like to know why. 

I've looked at the times she is sending the emails and they have been sent at all different times. 

I'd be grateful for any help or suggestions.  This is really frustrating.

Thank you to anyone who may be able to help.

[somegirl]

What is the reason listed in the bounceback email?