Using the mail in offline lets you to access your E-Mails in your Gmail with full control. You can get the app for free from Chrome Store. With one click you can install this Gmail Offline App by sign-in into Chrome with your Gmail account.
To add the Gmail Offline to your Chrome follow the below steps
Go the this link Google Gmail Offline App from your Google Chrome Browser
As soon as you enter to Google Chrome's Apps market you will be allowed to sign-in with you Google Email ID.
After Signing into the Google Chrome you will be allowed to Install the App on your chrome Browser by hitting on "Add to Chrome" (Please wait for some time to install the app on your Chrome Browser).
After installing the Google Gmail Offline app on your chrome browser you will be able to see you emails on your chrome browser even when your are on offline connection i.e with out internet connection
The User Interference of the Google Gmail Offline Apps is not same as Actual Gmail Interference. Of-course the user interference of this app is so easy to navigate and access all the option on your computer with out Internet Connection.
You can also compose the email from your offline gmail app in offline connection and the composed app deliverers to the as soon as your computer is connected to Internet.
And you need not to worry about the Security Issues as this app is developed by Google Itself.