Nope. NNTP-Posting-Host is inserted by news server, so it's nothing
to do with your newsreader. Moreover, if you try to insert one by
yourself, your message won't be accepted (probably).
It happens sometimes that this header is not added to a message,
mostly when you use a mail->news gateway. I don't think you should
worry - isn't this nice to be sometimes *completely* anonymous? :-)
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| . ) |/ / ------ Piotr K=EAplicz ------ \ \| ( . |
|__||_|\_\ http://rainbow.mimuw.edu.pl/~pkeplicz /_/|_||__|