Hi there, @bhibler.

This error is caused by an outdated Microsoft Office 365 release. To fix it, you can update your Microsoft Office 365 to the newest release version. Here's how

1. Open Outlook, then select the File tab.
2. Select Office Account, then the About Outlook button. Note: Make sure you see the latest release of the build.
3. Select Update Options and then Update Now to update the newest release.
4. Go back to QuickBooks and try to email your report or transaction again.

If the issue persists, you can follow these next troubleshooting steps:

Step 1: Edit your admin privileges

Make sure QuickBooks isn't set to automatically run as an administrator.

1. Close your QuickBooks Desktop application.
2. Click the Windows Start icon at the toolbar.
3. Type "QuickBooks" in the search, then right-click the QuickBooks icon and choose Open file location.
4. Right-click the QuickBooks.exe file and select Properties in the folder.
5. Choose the Compatibility tab.
6. Select to uncheck the Run this program as Administrator option. If the option is grayed out, select Show Settings for All Users to make the option available.
7. Click Apply and then OK.

Open your QuickBooks Desktop application and send a test email or transaction. If you still receive an error message or still cannot send an email, you can refer to this link for more troubleshooting steps: How to fix "Error: QuickBooks is unable to send your email to Outlook".

Let me know if you have more questions about connecting a bank account in QuickBooks Online.