I'll chime in and share some guidelines to help you fix this error using webmail in QuickBooks Desktop.

This issue has to do with email addresses. So we recommend multiple solutions that may resolve the issue. You can perform each solution presented, as the initial solution may provide a resolution, or further attempts may be necessary. We advise following these steps for optimal results.

First, update to the latest release of your QuickBooks to have the latest features and fixes.

1. Go to the Update to the Latest Release page.
2. Make sure your product is selected. If not, go to the Change link and select your QuickBooks product.
3. Select the Update button to download the update file.
4. Select Setup Automatic Updates to learn how to set QuickBooks to automatically download and install the latest updates.

For more details of the entire process, refer to this article: Fix Error: Could not connect to the email server.

However, if the issue persists, it is best to connect with our QuickBooks Desktop Support, as it may be a technical issue that requires assistance from our Customer Care Team. Contact them for further guidance. They also have tools like screen sharing and guide you through the process.

Here's how you can reach them:

1. Open QuickBooks.
2. Go to the Help menu at the top.
3. Select QuickBooks Desktop Help.
4. Type Contact Us in the search box. Then, click on Contact Us at the bottom.
5. Select the way you wish to connect with support.

Please refer to this article for additional details: Contact QuickBooks Desktop Support.

You can also visit this article for future reference: Fix webmail password issues in QuickBooks Desktop.

Please don't hesitate to reach out if you need assistance with QuickBooks-related concerns. Have a nice day!