Yes, there's a way to change the sending email address in QuickBooks Online. Before that, let me share some information on why invoices keep going to your client's spam folder.
It's a direct result of the Intuit's procedure of sending emails. With that, it's best to set Intuit’s service-related email addresses as a safe sender or whitelist it on your customer’s account for them to receive important communications.
Here are the steps on how to update your email address:
Go to the Gear icon.
Select Account and Setting under Your Company.
Click the Contact info section.
Enter your new sending email address.
Click Save. Then, Done.
Then, we can ask your customers to set a rule to allow that email address to go to the inbox. Check out these articles for further details: