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When using POP or IMAP accounts (ie. not with MS Exchange Server), you have to create another account in your Outlook configuration for the new identity. Then, depending on your Outlook version, you are presented with another 'From' address or an 'Account' selection to choose your 'From' identity.
Options
menu when creating a new message.Microsoft Exchange makes identity management possible with Outlook.
See the properties “Send As” vs. “Send on Behalf of”.
http://www.webville.net/kb/Knowledge%20Base/Multiple%20Identities.aspx
http://www.howto-outlook.com/faq/aliases.htm
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