Thanks for reaching out to this forum, AD2025.

To resolve this issue promptly, I recommend contacting our live support team. They have the tools to conduct a thorough review and help identify why your customers' email addresses disappear when using the Combine forms to a recipient in one email feature.

To contact them, here's how:

1. Open your QuickBooks Desktop.
2. Go to the Help menu and select QuickBooks Desktop Help/Contact Us.
3. Enter a topic or questions in the field provided or click the Contact Us button.
4. Follow the on-screen steps.

To learn more about our support hours, please visit this article: Get help with QuickBooks products and services.

While we address this issue, I suggest changing your email preference to WebMail to ensure you can retain your customer's email address. To do this, follow the steps below:

1. Go to the Edit menu, then select Preferences.
2. On the Preferences window, go to Send Forms.
3. Go to My Preferences, then tick the WebMail in the Send-Email Using section.
4. Once done, click OK.

If you have other concerns or questions, feel free to comment them below.