Unix "lifetime-mail"

[J.R.ter Haseborg <J.R.terHaseborg@tu-harburg.de>]

Hi,
does anyone know the kind of mail shown below?
It seems to be the unix time.
I receive this mails now and then and don't know which system service sends 
this mails and why.

Jan Remmer t.H.


Example:
------------------------------
Content-Type: 
Status: RO
X-Status: O

1 1000502681.9146
------------------------------