I feel your pain.
> Customer: My client didn't get the email I sent.
> Me: I can see that their email system accepted it.
> Customer: But my client didn't get it.
> Me: I'm afraid I can't help that; your email system did send the
> message, and your client's system accepted it.
> Customer: That's no use to me, I need people to get emails when I send them.
> Me: ...?
