My contractors still have not received their 1099s. Recipient copy says Mailed in QBO. How do I find out if they actually have been mailed yet?

Yes, there are many posts like this here, both for QuickBooks Online and QuickBooks Desktop.

It seems that for many customers either Intuit sent them late or didn't send them at all.

Welcome to the Community, @heathera-thealpe.

Currently, there is an ongoing investigation about the emailed 1099s that are not received. Rest assured that our Engineering Team is dedicated to working for them to implement a solution that will fix this issue.

Please know that this is a top priority for us. It will continue to be so until resolved.

I encourage you to contact our Phone support team. They can add you to our notification list, and you'll receive an email notification once an update is available. 

Here’s how:

1. Sign-in to your QuickBooks Online company.
2. Click Help (?).
3. Select Assistant tab to get started and get quick, personalized answers. Select a suggested option or type a question or topic you need help with. If you decide you need further help, you can still Talk to a human.

You can then choose a way to connect with us:

• Start a chat with a support expert.
• Get a callback from the next available expert.

Meanwhile, you can also print your 1099s in QuickBooks Online and send them to your contractors. 

For future reference, you can look closely at your business's finances by running a payroll report. Here is an article for the detailed steps: Run a payroll report. It will provide a detailed summary of your company's payroll expenses, including employee salaries, bonuses, taxes, and other related costs.

Let me know if you have questions about 1099. I'm always here to help. Have a great day.

@Ethel_A  RE: Currently, there is an ongoing investigation about the emailed 1099s that are not received.

The OP did not ask about emailed 1099's. Did you even bother to read the question?