- $xref =~ s/:[0-9]+//g;
- $hdr->header_set('Newsgroups', (split(/ /, $xref, 2))[1]);
+
+ # RFC 5536 3.1.4
+ my ($server_name, $newsgroups) = split(/ /, $xref, 2);
+ $newsgroups =~ s/:[0-9]+\b//g; # drop NNTP article numbers
+ $newsgroups =~ tr/ /,/;
+ $hdr->header_set('Newsgroups', $newsgroups);
+
+ # *something* here is required for leafnode, try to follow
+ # RFC 5536 3.1.5...
+ $hdr->header_set('Path', $server_name . '!not-for-mail');
+