The Exchange server in our environment serves two domains, DOMAIN01 and DOMAIN02. Users in DOMAIN01 are unable to connect to Exchange via Outlook. They receive the error message "The name could not be resolved. Network problems are preventing connection to the Microsoft Exchange Server computer. Contact your system administrator if this condition persists" followed by the error message "The name could not be resolved. The action could not be completed".
This issue was only affecting a limited number of accounts until a few days, it seems, but now all users in DOMAIN01 appear to be affected. It appears that the trigger for this behaviour is password reset / expiry on the accounts.
No accounts in DOMAIN02 appear to be affected.
Users in DOMAIN01 are able to access their e-mail via Outlook Web Access (OWA) successfully. The problem appears to be with the Outlook 2000 client.
We have observed that if, within Exchange, we selected "Exchange General\Delivery Options\Add\Send on behalf of" and add the users' own account, it appears to remedy the situation.
We have hundreds of users, so this is not a practicable solution ultimately, but I hope that it will give some hint as to the root of the problem.
It feels as though it is authentication / permission related.
I am tempted to discount firewall issues because there have been no changes at a network level. Additionally, firewall rules would affect all computers in DOMAIN01 equally and simultaneously. We would not have seen the gradual password-expiry related issue.