0x8004210B

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CAUSE
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This behavior occurs because some Internet service providers (ISP) do not permit message routing through another SMTP server while you are connected to their network.
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RESOLUTION
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To resolve this behavior, replace the SMTP server for the other ISP or the other e-mail account with the SMTP server that is associated with the ISP that you use to connect to the Internet. To do so, follow these steps:
Contact your ISP to obtain the outgoing SMTP e-mail server address.
Start Outlook 2002.
On the Tools menu, click E-mail Accounts.
Under E-mail, click View or change existing e-mail account, and then click Next.
Click the account that you want to change, and then click Change.
Under Server Information, type the name of your e-mail server that you determined in step 1 in the Outgoing mail server (SMTP) box, and then click Next.
Click Finish