[exim] Problem with MAIL FROM setting

Hi,

I have a problem where the mail sent by my Exim4 to some addresses fails
due to the MAIL FROM address being incorrect and failing reverse lookup.
For example:

SMTP error from remote mail server after
MAIL FROM:<www-data@???>

I have set in my /etc/hosts file for the domain to be the proper domain
and can't find any setting in exim config where it's set wrongly, does
anyone know how I can get rid of this phx.dedicated.codero.com out of
the system?

Thanks,
Aran