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Read about how to enable your Gmail account to send from another address in the Gmail Help Files.
http://mail.google.com/support/bin/answer.py?hl=en&answer=22370
Hotmail
- Click Options.
- Click More Options.
- Click Send and receive mail from other e-mail accounts.
- Click Add another account to send mail from.
- Enter your McCombs address and click Send verification e-mail.
- Check your McCombs account. If you've graduated, check the account where your McCombs email is being forwarded.
- You will receive a verification email from Hotmail. Click the verification link in the message.
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Read about how to enable your Yahoo account to send from another address in the Yahoo Help Files.
http://help.yahoo.com/l/us/yahoo/mail/original/manage/sendfrom-01.html