Empty mail

[redyuck]

Server send me two empty mail:

log:
root@srv [/var/log]# cat exim_mainlog | grep 1NIP8u-0002b8-6P
2009-12-09 13:11:56 1NIP8u-0002b8-6P <= xx@srv.domain.com U=user P=local S=504
2009-12-09 13:11:56 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1NIP8u-0002b8-6P
2009-12-09 13:11:56 1NIP8u-0002b8-6P => user <user@domain.com> R=virtual_user T=virtual_userdelivery
2009-12-09 13:11:56 1NIP8u-0002b8-6P Completed

And the mail

Precedence: auto_reply
X-Precedence: auto_reply

what happen with my mail server ?