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Google's free email service Gmail allows free IMAP access. This means you can use a an email client like Thunderbird installed on your computer instead of opening http://www.gmail.com in your web browser to access Gmail.

Here's some quick reference for setting up IMAP.

User Name: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Incoming Server: imap.gmail.com (SSL port 993)

Outgoing Server: smtp.gmail.com (TLS port 587)

Source: http://mail.google.com/support/bin/answer.py?answer=75726

Invalid Credentials Error (Failure) / Web Login Required

For email clients connecting to Gmail via IMAP or POP, sometimes you might get this error during login. Visit https://www.google.com/accounts/DisplayUnlockCaptcha to clear the CAPTCHA. You should be able to login after that.

Source: Fix Gmail IMAP Invalid Credentials or Web Login Requires (Failure) Error