This is an issue with the way authorize.net generates the issue, there is not something that can be done in eCart to hcange this.
If you are using the SIM implamentation method with authorize.net, the order is not processed in real time, meaning that the transaction is not appoved for success or failure until Authorize.net have cleared the transaction, you should not be relying on that initial email for notification to ship, you should be relying Authorize.net clearing the transaction before you ship.
if you use the AIM method, that is a real time payment method, if you also have data bridge, you will be able to configure universal email to send a receipt when the transaction is placed.
