How can I tell if this is a fraudulent invoice? I don't recognize the charge and didn't open file

Thanks for reaching out to us here, winterplum.

I'll share some information on how you might identify any fraudulent activities to protect your business from a fraudster.

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Getting suspicious emails can sometimes be a scheme to get you to share your personal information. If you’re unsure that an email came from Intuit, you can check out these information:

• We’ll never ask for your personal info in an email.
• Our emails will always come from an email address that ends with @intuit.com. This includes @e.intuit.com.
• Any link we send you in an email will always be for an intuit.com address.

You can also read these articles for more details: 

• Identify suspicious activity and phishing scams
• Official email communication from Intuit Payments
• How you can help protect your business from fraud

Please let me know if you require additional information or other concerns with your QuickBooks Online account. I'll be round to help you out again. Take care!