I'm not receiving undelivered email notifications. Why?

When your email gateway (sMTP) tries to send a non-delivery report to our mail server, the report may be blocked when the sender domain is empty.

To make sure bounce notifications arrive in Collections, please whitelist these IP addresses.

Start	End (inclusive)
109.68.163.1	109.68.163.59
109.68.163.129	109.68.163.187
109.68.163.193	109.68.163.251
109.68.167.97	109.68.167.123