Watchguard V10 User Manual page 312

CHAPTER 10: Using Proxies
Headers tab
This tab allows you to specify values for incoming SMTP
Header filtering.
Header Rules
- Approved-By
- Bcc
- Cc
- Comments
- Content-Description
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This ruleset allows a number of SMTP Headers.
The default rule strips all other SMTP headers. As
there are hundreds of possible SMTP headers, it
might be useful or necessary to allow other SMTP
headers in your system.
The Headers that are allowed include:
Vcontroller