For the last couple of weeks, my boss and I have been trying to figure out a customers email problem.

She sends and receives all her email fine. Except, she can't receive from one client. It's not getting tossed into SPAM, (we're not that dumb). The sender get's no 'failed to deliver' message.

We have been online with our customers host, and the email doesn't even hit their server. We are still waiting to hear back from the senders host to try the same test.

We had the sender send us the email and also the client. We didn't get it but the client did.

We had the sender put our clients address first, and ours second, and we got it but the client didn't.

When our address was first, but the client was in the CC field, we both got it.

So, it boils down to: the first address in the 'To' field does not get the email, unless there is an address in the 'CC' field.

Anyone have any ideas of how to fix that?

Oh, and it only happens with our client. The sender has no issues sending to any one else. And our client has no issues receiving from anyone else.

I swear, if I had hair, I'd be pulling it out....