Can we send an instant reply message in an email client?

All you have to do is to configure Auto reply rule in your Microsoft Outlook. Here's the easiest way to do it: Open your Microsoft Outlook and go to the Tools menu and then choose Rules and alerts. 

 

Choose the new rule category; select Start from a blank rule and click Next. In Rules Wizard, check this: where my name is in the To or Cc box, and click Next again. Also check the box: have server reply using a specific message. In the bottom box, click the underlined link a specific message. After you are done, a blank e-mail message will appear, and this will be your Auto reply e-mail that will automatically be sent to your senders.

 

Now you can customize this message the way you want it by filling in the subject and the body of the message. 

 

When you are finished, Save and Close your e-mail, and after that just click the Next button twice. Don't forget to check this rule: Turn on this rule, and click Finish and then OK. 

This should be it.