Your correspondent received a bounce message but overlooked it
In this situation, someone sends you an email but receives a Non Delivery Report (NDR) which they overlook and then chase you for a response to the email you never received. The reasons for a NDR are many – for example, their email may have been rejected as spam or because it contained a disallowed file.
How to fix:
- If you need to prove that they received a bounce message, please ask your email administrator to check the email logs.