Exchange 2013 - SEND AS permissions - How does outlook decided whether to SEND AS or SEND ON BEHALF

Currently trying to test this.

1. Gave myself FULL ACCESS and SEND ON BEHALF permission to test user. Result - Emails SENT AS.

So, do you need SEND AS if you've already got FULL? How does outlook know when to SEND ON BEHALF?
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Alexei KuznetsovMicrosoft Outlook MVPCommented:
You may want to convert it to shared mailbox. Hopefully this will help.

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Outlook with the mailbox added to one main account (added to your own email account), is usually Send As.

Outlook with the mailboxes each separately added as  accounts (Since Outlook 2010), Send full (remember, when you add mailboxes, each as a full account, you tell the Exchange server usually your OWN username, therefore when you add it, even if it's its own account, you need full mailbox rights as well as full send rights)
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