Why do invoices sent through QuickBooks go to receivers spam/junk mail?

I can share some information so the invoices you sent, @colette-boldy2.

It's possible that QuickBooks is blocked by your customer's email provider. Blocked email notifications are redirected to their spam/junk folder. First, let's review the email address set up in your account. Here's how:

1. Go to the Gear icon ⚙️.
2. Choose Account and Settings.
3. In the Contact info section, review each email address.
4. Make changes as needed.
5. Select Save and then Done.

Once completed, send yourself a test transaction to test it. If you’re getting the same result, you’ll have to use a different email address that has a different domain. 

If the issue persists, you can perform the second and third solutions on this article: 3 Solutions For When Customers Aren't Receiving Your Emails.

On the other hand you'd want to make sure 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. 

Also, you can follow the troubleshooting suggestions for your email provider in this article: How to make sure you receive important email messages from Intuit. 

I'll assist you again if you have other things to do in QuickBooks. Post them here or create a new thread in the Community and I'll be right there with you.