When you try to use Microsoft Entourage to send an e-mail message through a Microsoft Exchange Server computer, you may receive an error message that resembles the following, where "name" is the account name for the Exchange Server account:
HTTP error: Access to the resource is forbidden.
Mail could not be sent
Account name: "name"
This issue occurs if the account e-mail address in Entourage does not match the Simple Mail Transfer Protocol (SMTP) address for the user in the Active Directory directory service.
To resolve this issue, change the account e-mail address to match the SMTP address in Active Directory. To do this, follow these steps:
On the Tools menu in Entourage, click Accounts.
Click your Exchange Server account, and then click Edit.
In the E-mail address box on the Account Settings tab, type an e-mail address that matches the SMTP address for the user in Active Directory, and then click OK. You may have to contact your system administrator to obtain the correct e-mail address.
The information store on an Exchange Server computer tests for e-mail spoofing. E-mail spoofing is constructing an e-mail header so that it appears as if the e-mail message came from someone other than the actual source. If your e-mail address is not authentic, the information store will not authorize you to send e-mail through the server.