I used to be able to send invoices out through email in QuickBooks.

You can resolve this issue with the help of the below-given steps:

Ensure that Email Preference has been correctly set in QuickBooks

If you use Microsoft Outlook with Microsoft Exchange Server, then Open Outlook and sign in before you start checking the preferences set in QuickBooks.

• Select ‘Edit-> Preferences -> Send Forms‘
• Now click on the ‘My Preferences‘ tab and set ‘Send E-mail using’ and the option you want to use. Then, click ‘OK‘.
• If you find the preference to be set correctly, then follow the following steps:
  • Choose ‘Edit -> Preferences -> Send Forms’
  • Choose the tab of ‘My Preferences‘ select ‘QuickBooks E-mail‘ and Click ‘OK‘.
  • Click on ‘Edit -> Preferences‘
  • Select ‘Outlook‘ and Click ‘OK‘.
• Now, close QuickBooks and other programs.
• Restart Windows and then, restart QuickBooks
• Now email the report.