[exim] strange connection?

Hi all,

I my mainlog at every SMTP connection, I get a 'no IP address found for host
xxxxxxx.free.wxs.nl (during SMTP connection from..' and then the hostname
and IP# of the sending host, which is completely different. I'm not
connected to wxs.nl, but this message turns up at every connection and the
xxxxxxx above is always the same number.

Does anyone know what this could mean?

Cheers,
Thijs