You want to setup two custom recipients; one for monkey and one for grinder and you also want to add alternate recipients to the sales mailbox.
Setting up monkey and grinder:
Go to Exchange Administrator?s File menu and click New Custom Recipient.
Select the type of address (internet), click OK
In the Internet Address Properties form enter the forwarding address (monkey@gwis.com for one account and Grinder@aol.com for the other) and click OK.
Next you will see the property pages. Enter the appropriate General info and then select the E-mail Addresses tab and click new- Internet address and add the mailbox address of the user (monkey@mydomain.com for one and grinder@mydomain.com for the other) and click OK. This should accept mail to these mailboxes and then automatically send them to the Internet addresses.
Setting up mail forwarding for sales:
I know that the following will send mail from one account to one other account but I?m not sure about sending it to two other accounts (i.e. from sales@mydomain.com to monkey and grinder). You can go to the sales mailbox properties and select the Delivery Options tab. Any mailbox entered into the Give Send On Behalf of permission to list will be able to respond on behalf of the sales mailbox. At the bottom of the form you will see Alternate recipient, I believe (I?m not sure) you will see both mailboxes listed next to the modify button (if you listed them in the Give Send list). Make sure that the Deliver messages to both recipient and alternate recipient check box is checked. This will allow the listed mailboxes to both receive and respond to mail sent to sales. If the check box is not checked then only monkey and grinder will receive the sales mail.
Hope this works, it's been a while since I tried this stuff.