Site contact question

We launched our site in Xaraya last week.

In the site contact we have introduced two forms. The forms has been tested,
and worked as expected.

Yesterday i got two responses in the database on one af the forms. One of
the respondents complains, that the response was returned with an error.
(The form forwards responses to an external e-mail)

The only difference between the two responses i can see, is, that for the
one with complains, there are no IP address in the database. A possible
reason for the complain, could be, that I somewhere have a tricker
insisting on an IP address from the user, as a prerequisite for forwarding
mails. It makes sence, but then I would like to know what i have done. 

I have asked the user for further information, but would like to put the IP
question here.

Regards
www.tolvege.dk - a major step for us, but nothing special as such.

Jørgen