I already have my main email address added to the "Manage forwarding email" section but how can add one more email address which I receive 5-10 receipt emails per day

Hi, Mark. Currently, you can register only one email address per user for your company in QuickBooks Sole Trader.

However, you can Update this email as part of your Intuit account information. Please note that changing the email address could interrupt email forwarding.

Make sure to notify all registered users of the new email address, and remember to update your email auto-forwarding settings accordingly.

You can check this article for more information: Email receipts and bills. While it is a QuickBooks Online article, the process is similar in QuickBooks Sole Trader.

If you have any further questions, please don't hesitate to reply below, and I will respond promptly.