Hmm, looks like the problem is not with my webserver. I tried with
sending emails to non existent users on my mailserver from my mail
account on http://gmx.net When I use any other provider the date is
correct and also when I sent to non existent mail addresses from on
other mail servers from my gmx account I get the 1.1.1980. So it looks
like there's a problem with gmx's qmail and not with my FreeBSD/postfix
system.
Thanks for your anyway.
Gunnar