http://support.google.com/mail/bin/answer.py?hl=en&answer=21289

To set up Mail Fetcher:

  1. Click the gear icon  at the top of any Gmail page, choose Mail settings and open theAccounts and Import tab. (For Google Apps domains, open the Accounts tab.)
  2. In the Check mail using POP3 section, click Add POP3 email account.
  3. Enter the full email address of the account you'd like to access, then click Next Step.
  4. Gmail will populate sample settings, but we recommend checking with your other provider to learn the correct server name and port. Enter your Password.
  5. Decide whether to:

  6. Leave a copy of retrieved messages on the server

    Always use a secure connection (SSL) when retrieving mail

    Label incoming messages

    Archive incoming messages

    1. Click Add Account.
    2. Once your account has been added successfully, you'll have the option of setting it as acustom From address. This allows you to compose messages in Gmail, but have them appear to be sent from your other email account. Click Yes to set up a custom From address.