You could check the status of email delivery by getting into ' 'Email History' under the 'Customers' tab.

For example, if you wish to see the status of the invoice emails, you could click the "Show" drop-down filter and can select Invoice Notification from the list.

Alternatively, you can 'CC' yourself while sending Invoice mails to customers. See how:

• Click the Settings tab.
• Click the Invoice Notification sub-link under Email Settings.
• Check the box next to "CC me on invoice notifications".
• Once this is done, click on Save.