First, you'll want to check your spam or junk folder. If you can see them from there, simply click This is not spam or Not Junk. This will let your email provider know that the emails from QuickBooks Online are legitimate and won't be tagged as spam again.
Also, some email providers may block the @intuit.com domain. You'll want to send an email to do_not_reply@intuit.com so that they'll recognise that the said domain is a trusted one. You can also add do_not_reply@intuit.com to your contact list or address book.
In addition, you'll want to check if the email entered is correct. If the same thing happens, I suggest you reach out to your email provider's support to see if there's an issue on their end.