HOWTO fix "You do not have permission to send to this recipient."?

This is a mailbox permission issue.  Here's the step by step procedure to assign the permission.

For example.
John King will give permission to Mary Queen to open his mailbox and send on behalf while he's out.

1. Open Active Directory (AD)
2. Go to the User OU, right click on John King properties
3. Click Exchange Advanced, click Mailbox Rights.
4. In Mailbox Rights, click Add Mary Queen, and give Permission
5. Put check on Delete mailbox storage, Read permissions, Take ownership, and Full mailbox access. Click OK
6. Click Exchange General
7. Click Delivery Options
8. In Send on behalf, click Add Mary Queen, then click OK

We just completed giving the right permission to Mary Queen to access John King mailbox. Now let's add John King mailbox to Mary Queen outlook.

1. In Mary Queen Outlook, click Tools, then Options.
2. In Options, click Mail Setup, click E-mail Accounts, click Next.
3. In E-mail Accounts, click Change, click More Settings
4. In Microsoft Exchange Server, click Advance tab, click Add.
5. In Add Mailbox, type John King, click OK to close.
6. Click Next, Finish.

Testing:

In Mary Queen Outlook, you should be able to see another Mailbox - John King. You should be able to see John's mailbox folders, and be able to send on behalf.

If you have questions or suggestions, please post it here. 

Thank you.