Outlook 2010
Open Outlook. Click the File tab on the ribbon and then click Info on the left.
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Select your email account from the list, then click Account Settings and choose Account Settings in the menu that appears.
Select your email account and click the Change button.
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Click the More Settings button, then click the Outgoing Server Tab
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Check the box that says "My Outgoing Server (SMTP) Requires Authentication. Make sure the box below it that says "Use Same Settings As My Incoming Mail Server" is also checked.
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Click The Advanced Tab and change the Outgoing Server Port number from 25 to 587.
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Click OK, click Next then click Finish.
You're done!