Sending your customer their invoices by email is a great way to save time and track the status of your customers invoices. I'd be happy to help you with stopping your invoices from showing up every month.
If the email is being sent around the same time every month and showing up in your QuickBooks even though you deleted it sounds like you may have it set up as a Recurring Transaction. This would send the email out every month as well as add it back into your QuickBooks Online. You can check for any recurring transactions by going to: Gear>Recurring Transactions. Once there you can remove it from the list to prevent it from sending out again.
If you have any questions let us know and we'd be happy to help.
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