Problem
Need to be able to Send As a mailbox in Outlook on an Apple Computer, iMac or Macbook
Environment
MacOS Outlook
Resolution
Prior to the next step you will need to get "permission" to Send As to a certain mailbox.
On an iMac or Macbook open locally installed Outlook.
Go to the “Tools” Menu.
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Click “Accounts”'
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Click on “Advanced”'
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Click on “Delegates” Tab
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Add the mailbox under Open these additional mailboxes Click the “+” Office 2016
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Type the mailbox name of the person, group or resource (including Distribution List) whose mailbox you want to be a Delegate for and add to your user profile.
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Pick the proper permissions needed.
Click Find, OK, OK, Red X in the upper left to close.
Note: Relaunch Outlook. If you don’t see the mailbox right away, it may take a few moments.
Cause
Delegates/Additional Mailboxes need to be added manually