Previously in Facebook i have seen the option for deactivation but don know whether that option exist for normal mail account. Anyhow just see the settings option in you mail account or profile.
Wow till now dropping the mail id means i used to think that change the password and throw it some where so that we wont remember it. but you have given me a good idea thank you sasikanth
If you want automatic deactivation, then you can wait for two to three months without logging in with that particular account and it will automatically get deactivated...!