I want to make sure you're able to email invoices to customers, Jrountree.

The verification may have been turned off, and that's why you're unable to send invoices via Yahoo! Mail.
 

Yahoo Mail uses a 2-Step Verification process. That being said, you need to review their security settings.

Here's how:

1. Go to your Yahoo Account Security page.
2. Turn on the Two-step verification and Allow apps that use less secure sign in features.
3. Go back into QuickBooks and email yourself a test transaction.

If you still can't send emails, use Yahoo's generate third-party app passwords tool. It creates a random password you can use to connect to QuickBooks. You only need to do this once.

If you’re batch sending emails, the password will expire after sending 12 invoices or transactions. You’ll need to generate a new third-party app password to continue.

1. Follow the steps to get a password.
2. Go back into QuickBooks and email yourself a test transaction.
3. In the Password field box, enter the third-party app password, then select OK.

To send email to QuickBooks, Yahoo mail powered by AT&T now generates a secure mail key when sending emails via the third-party desktop app as its new feature.

Also, you'll want to check if the antivirus software may have accidentally block the connection. Search your antivirus provider's website for steps to allow port exceptions. Here are steps for Norton and McAfee. 

If you use McAfee, open your antivirus program and check your Excluded Processes list. Add these names to the list so they can run freely.

• QBW32.exe - C:\Program Files\Intuit\QuickBooks [year]\QBW32.exe
• QBDBMGRN.exe - C:\Program Files\Intuit\QuickBooks [year]\QBDBMgrN.exe
• QBDBMGR.exe - C:\Program Files\Intuit\QuickBooks [year]\QBDBMgr.exe

Go back in to QuickBooks and set up again the connection. Make sure to use Port 465 for Yahoo! Mail. Then, email yourself a test transaction.

Here's an article as a guide: Learn how to set up your email service in QuickBooks Desktop. It includes what SMTP server and port to use for Yahoo Mail.

If you're still unable to send emails, I recommend getting back in touch with our Live Support Team. I know you've already contacted them. However, they can create a case to further investigate the issue.

Don't hesitate to post again if you have other QuickBooks concerns aside from sending emails to customers.. I'm always around here in the community Forum to help you.