[horde] Login / IP issues?

[Ian]

Hi,

I have a setup of IMP4 on a plesk based server.

We have a user who is behind a proxy/load balance connection - as such every
hit on the server changes his IP address, this in turn is causing it so that
he is unable to actually login (unless he is very lucky)

Cookies are being set on his computer - but not able to hold a connection.

Is there any settings that can be altered to allow for this?

Thanks.