mailx in pipeline mode: add fields to the EMail header?

Hi folks,

is there some way for OpenBSD's mailx (reading an EMail to send from
stdin) to add fields to the EMail header, e.g.

Auto-Submitted: auto-generated

for generated EMails, according to the recommendation in RFC 3834?
Or maybe

Precedence: bulk

Maybe some custom fields like

X-monitoring-severity: disaster
?

This could help to avoid a lot of unnecessary vacation responses,
support automatic filtering, etc.

The mailx command line could be

echo hello | \
mailx -s hello -a "Auto-Submitted: auto-generated" jack@example.com

I thought about making "Auto-Submitted: auto-generated" the default
for reading an EMail from stdin (if its not a tty), but this might
break existing code.


Regards

Harri