@ray fradge The solution you suggest would work if the emails were being allowed through the servers but they are not. It is not a case of them dropping into the customer's spam folder or of the customer's emailer software blocking them. The invoices don't get that far -  they are being blocked at server level. and to compound the problem this means our QBO software doesn't get a hard bounce so we have no clue that our sales invoices haven't been received - until the customers don't pay.  Worse still, some invoices get through and others do not. And sometimes a few will get through to a particular customer and then some don't and then they start getting through again. So customers may pay earlier and later invoices and then you can't match it up becuase there are a batch in the middle they haven't paid.  The servers must be continually re-listing the QB domain as a sender of spam, presumably in some sort of automated process. Nothing our customers can do will fix this issue. Only QB can fix it - very simply by allowing us to use our own corporate emails to send out our sales invoices.