Perhaps you should try mailing your invoice - in an envelope, with a stamp.  Email is so unreliable - I have had clients that I regularly correspond with via email who suddenly end up in a spam folder.  No idea why - but it happens.  

I will frequently follow up an email with a good old fashion letter.  Not that U.S. post office is the greatest, either, but at least it increases your chances that it will get through one way or another. 

And, it seems to have worked for Naomi. 

Best,

Robert A. Franco
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