Hi, Kitty,

The settings appear to be correct.

I'm wondering if there could be some sort of 'spam protection' that's kicking in when the range of invoices are sent -- either on your end or the customers. Are there basically the same number of customer invoices sent out each time or does this vary?

If the customer was never receiving the attachment, I'd suggest that perhaps they were using an older version of Adobe Reader than your office but you say that whether or not a customer receives the attachment seems to be more random.