All I need when I buy something online is the shipping tracking number. That's it. I don't need an invoice. What am I going to do with that, print it out and stare at it? I don't need constant tracking updates. I can get these myself with the tracking number. I don't need to know it was delivered (again, tracking number, and I can also just look on the porch with my eyeballs). I don't need any of the other sales-spam that always seems to accompany these orders. An online merchant shouldn't even need my E-mail address. I should be able to click "buy" and the next page shows me the tracking number. That's the only relationship I want with you!

An invoice/receipt is often necessary for booking purposes, reimbursements, taxes, etc. But to your point, just put it in the same email as the tracking number and move on.

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