Gmail: What are ways to schedule email to be sent later automatically using Gmail?

We are using Gmail for email communication since a long time. There is no default option in Gmail to schedule an email for future date and time. Gmail is missing the ability to schedule when an email gets sent - you must click the "send" button at the exact moment of delivery. How is it possible to schedule outbound email to be sent at any future date and time using Gmail? I ask myself - Is there a free email scheduler solution for Google Apps for Business, too? (Solutions for Gmail without using an external email client like Outlook!)

Then i do research for this solution and got a lots of third party apps and extension for a browser to schedule Gmail - and i extract best 2 extension from the list.

1.Boomerang for Gmail
Boomerang for Gmail is a Firefox / Chrome plugin that lets you take control of when you send and receive email messages. For Firefox 3.6+, Chrome 5.0+ and Safari 5.1+. Works with Gmail and Google Apps email and supports upto 57 international languages.

With Boomerang you can:
Send an email later
The best follow up reminders
Remind you if you don't hear back
Other Value added Features in Boomerang:
. Remember to pay bills
. Schedule birthday/holiday notes when you have time to write them
. Make sure you follow up with a sales lead
. Communicate with people in different time zones
. Clear out travel confirmation emails, returning them on the day of your trip
  And lots more!
Boomerang are available in free and paid versions for individual and business and now also available for mobile version of Gmail.

To Download Boomerang for your Browser - install now


2.Right Inbox for Gmail
Right Inbox is for Google Chrome and Mozilla Firefox. Install it in 30 seconds and enjoy many useful features added to Gmail. Schedule Emails and send later.

With Right Inbox you can:
. Schedule Emails in Gmail To Be Sent Later
.Email Reminders in Gmail
.Track sent emails - Get notified when it is opened
 .Right inbox are also available in free and paid versions. In free version you can schedule 10 emails per    month.

To Download Right inbox for your Browser - install now

Security: Are you thinking about data security. There is no security lapse in using these 2 extension's - only takes the header section of your email i.e. sender ID, subject, date and time to deliver the mail. It doesn’t save body content on its server, so you don’t need to worry about the security.