Hi there, @ imagemarket.

I appreciate you following the steps above provided by my colleague so you can send an email invoice using your default email address.

Allow me to share other solution to set up a default email address when sending forms via Outlook. You can use Internet Explorer and reset your email preference from there.

Here's how:

Step 3:

1. Close QuickBooks account. 
2. Open the Internet Explorer.
3. Select Tools then the Settings menu and then Internet options.
4. Click the Programs tab. Then select Set Programs.
5. Choose Set your default programs. Then select the email service you want to use.
6. Hit Apply then tap OK.
7. Close the Internet Explorer. 

Once done, you can now open your QuickBooks account then send test email transactions. 

If you're getting the same result, move on suggested solution Steps 4 and 5. Check out this article for more detailed steps when seeing an error message about Outlook in QuickBooks Desktop: How to fix "Error: QuickBooks is unable to send your email to Outlook.

After the following steps above, I'd recommend contacting our Customer Support Team. You may also reach out directly to an IT professional for fixing Microsoft Outlook.

Thanks for your patience. If you need further assistance with the workaround, just let me know. I'm here whenever you need more help.​