Can receive email but not send it (since installing/uninstalling Zonealarm personal firewall)

Hi,

I am running MS Outlook 2000 on my home PC with Windows XP installed.  About a week ago I installed Zonealarm personal firewall.  All seemed OK until I tried to send an email and it repeatedly came up with the message:

"The message could not be sent because one of the recipients was rejected by the server.  Server response: '553 sorry, that domain isn't in my list of allowed rcpthostsn (#5.7.1)'.  (Account: 'me@myisp', SMTP Server: 'smtp.myisp.co.uk', Error Number: 0x800ccc79)."

I have since uninstalled Zonealarms, as I figured that it must have been something connected with this, but I am STILL getting the error - can anyone advise?

I did try to roll-back, but didn't create a new restore point prior to installing Zonealarms (D'oh - lesson learnt!!).

Hope someone can assist...

Steve