Delivery issue with invoices All clients I emailed before . Now every single invoice I send shows delivery issue.

Let's perform some troubleshooting steps to send the invoices successfully to your clients, info-machealth-c. 

The Delivery Server Down error is caused by attachments on your transaction or the way your Company email information is set up. Let's try checking if the email address format is correct in the location tracking information (skip if you're not using location tracking). Here's how: 

1. Go to the Gear icon at the top.
2. Under Lists, choose All Lists.
3. Tap Locations.
4. On the Run report drop-down, hit Edit.
5. Verify the email under This location has a different email address for communicating with customers. bullet and make changes as necessary
6. Press Save.

Once done, try turning on or off the Attach Invoice as PDF option in the company settings. Just follow the steps below: 

1. Go to the Gear icon on the top menu. 
2. Under Your Company, select Account and Settings (or Company Settings).
3. Select Sales.
4. In the Online delivery section, select or uncheck PDF Attached.
5. Select Save then Done at the bottom.
6. Send your forms.

For other troubleshooting steps options, you can check out this article: Delivery Errors when trying to email a sales form. Feel free to visit our Invoices and payments page for more insights about managing your sales transactions.

Do you need more help completing other tasks in QuickBooks? Please let me know and I'll assist you with some guides and other pointers. Have a great day.