[BlueOnyx:19477] Roundcube problem sending email

[Colin Jack]

We have installed the Solarspeed Roundcube WHAM but all the users cannot send email using RC.

Getting "Relaying denied. IP name lookup failed [192.168.10.254]"

Our servers are behind a firewall and that is the IP of the LAN interface.

It is only with roundcube that we see this - users using smtpauth can relay mail through this server quite happily.
NAT is all setup and working fine. HELO looks fine:

>>> EHLO pegasus.mainline.co.uk
250-mail4.vsn.voltage.com Hello pegasus.mainline.co.uk [87.127.234.5], pleased to meet you

Any ideas? I'm a bit stumped as to why it is only Roundcube (so local IMAP) that has this problem.

Colin