I want to connect my client application to one of the inbox of mail in a box is there a way which helps me to do that? If so how can i get the credentials for the same?
You set the credentials in the admin page.
Once they are set I’m not sure that decrypting the existing password is supported. You would need to set them again if you forget the password.
Use the admin page to get server information, which can also be used to tell you how to setup the mail client. Many mail clients support autoconfig/auto discover so if you put your email address in the client it can pull the server info using dns.