How do you manage email delivery failures? We are getting a lot of complaints from customers to say they are not receiving all invoices sent by email. Communications tab shows that they were all sent as expected, and I have check both the 'Undelivered Emails' and 'Bounced Email Addresses' pages and cannot see anything for the email address being sent to. Typically customers are getting some, but missing more than they receive (the last one I looked at received approx. 30% of the emails sent over the last month).

We have set up the DKIM records, and they appear to be testing as correct.