'no information' on availability of users in a meeting request

[thofram]

Hello,

I hope you can help me with the following question:
For the meeting-rooms and other recources of the office, I've setup a
mailbox for each resource (exchange 5.5). Nobody logons to those
mailboxes, only the reception-users have have them added to there
outlook (outlook 2000).

How can I make those mailboxes' calanders publish free/busy
information for more than the standard 2 month?

Thanks in advance.
Thomas