[Dovecot] dovecot+exim4+thunderbird+shared-folders-with-links+permissions-problems

[Uwe Fechner]

Hello,

I'm using 0.99.14 with debian 2.6.8-2-386 #1 Tue Aug 16 12:46:35 UTC 
2005 i686 GNU/Linux and
exim4.

I use the shared folder with symlinks, created by the script 
create_dovecot_shares-1.06.

I have set the permissions and use umask 0007 on dovecot  and
in exim in maildir_home:
  directory_mode = 0770
  mode = 0660

every thing works well, but

if I'm moving a mail from my inbox with thunderbird into the shared mailbox
it gets permissions
-rw------- 1 user group  11811 2006-12-09 12:58 
1165785386.P10056Q2M666099.blupp:2,Sa

instead of
-rw-rw---- 1 xxx group  31970 2006-12-10 17:26 
1165767986.H344527P28279.blupp:2,Sb

What am I doing wrong?

kind regards

Uwe