The IP address 255.255.255.255 appears in the following reports even if they are filtered to show outbound traffic only:
Top Sender HELO Domains
All Top Sender HELO Domain reports are affected
Top Sender IP Connections
All Top Sender IP Connections reports are affected
Top Succeeded Connections SMTP report
Top Failed Connections SMTP report
Top Rejected Connections SMTP report
The process of IP selection described in the "Sender HELO domain or IP connection shows gateway information" issue of the "Table: Report data details" section of the article HOWTO53390 is applied to all messages regardless of direction.
The IP address of 255.255.255.255 is used to indicate that the receive headers could not be parsed successfully.
This is by design.