I can share additional information, @JFazz.

Let's start by making sure that your QuickBooks software is updated to the latest version. This helps fix common QuickBooks errors and issue such as the inability to send invoice as an email.

Here's how:

1. From the QuickBooks▼ drop-down menu, select Check for QuickBooks Updates.
2. If a newer version is available, click Install Update.
3. When prompted, select Install and Relaunch.
4. When the update is complete, QuickBooks for Mac automatically opens.

Then, let's make sure your email account is setup as the default email reader from the Apple Mail menu. This ensures the program sends your sales forms through the default email account. I'll show you how. 

1. Select Apple Mail.
2. Choose Preferences. 
3. On the Preferences pane, click General.
4. Choose the email provider as your default email account.
   • If not, set your default email reader to Gmail, Yahoo mail etc. 

Also, you can go back to your Preferences to make sure that you're able to setup a default email reader by performing the steps below.

1. Go to QuickBooks from the top menu.
2. Select Preferences.
3. Click the Email icon.
4. Choose Custom from the Send Emails Using button. 
5. A list of email accounts will appear. Click the + button to add a new account.
6. Enter a name for the account.
7. Add the settings from your email provider.
8. Just repeat the process if you'd like to add any other accounts. 

Once done, email your invoices again. I've added this wonderful source that will provide you videos, articles, and advice when using QuickBooks Desktop Mac. You can browse our Intuit QuickBooks for Mac Little Square page.

Let me know if you have other concerns in the comments below, and I'll be sure to take care of them.