Why is quickbooks showing me error when i try to send an invoice via email despite my correct email and password?

Hi there, @designerslaborat. 

Thanks for visiting the Community. One of the reasons for this unusual behavior could be due to an incorrect setup of the server.

I'm here to help ensure you're able to send an invoice or any outgoing email through QuickBooks successfully. If you're using Yahoo! powered by At&t, follow these steps below to verify the email settings in your QuickBooks: 

1. In the Edit menu, choose Preferences.
2. Go to the Send Forms tab, then select My Preferences.
3. On the E-mail IDs section, click your Yahoo email and click on Edit.
4. Choose Others as the Email Provider.
5. In the Server Name field, enter smtp.mail.yahoo.com.
6. Use 465 or 587 as the Port number, then check the SSL/TLS box.
7. Click OK to save. 

Then, send a sample email to yourself to see if it works. 

If you're receiving an error when sending emails from Quickbooks using Outlook, make sure that your QuickBooks isn't set to automatically run as an administrator. Here's how:

1. Close your QuickBooks Desktop.
2. Go to the Windows Start menu.
3. Enter "QuickBooks" into the search bar, then right-click the QuickBooks icon and select Open file location.
4. Right-click the QuickBooks.exe file and click Properties.
5. Select the Compatibility tab.
6. Make sure to uncheck the Run this program as Administrator option. If the option is grayed out, select Show Settings for All Users to make it available. 
7. Click Apply, then OK.

Then, open your QuickBooks and send a test email to yourself. If you still see an error, edit your email preferences in QuickBooks by following Step 2 outlined in this help article: How to fix "Error: QuickBooks is unable to send your email to Outlook".  

Also, check out this help article: Fix Error: Could not connect to the email server. It has complete steps in fixing errors in case QB is unable to send form due to the inability to connect the email server. 

Let me know if you have additional concerns. We're always delighted to help.