replyPUSH is an email relay service, which enables you, the customer to receive email replies of transactional emails from your users, your site or application has sent out to them. The replyPUSH service sends back the replies as a notification reply in HTTP POST1, a way that can be processed easily for your purposes, without needing email receiving infrastructure.
The service processes email messages from your users, authenticates them using the your account credentials provided to the you via the website account profile, and sends the message, other data and select headers to the provided public Notification URL2, through a HTTP POST.
Replies can be received via the service email address, because a special email header field instructs the email client to reply to this address (provided documentation is followed).
The service can be used for a variety of applications but is primarily focused toward community / social software in order to send email replies back to the community / social website, to “post” these replies in context.
Your users are normally replying to a transactional email sent out with the special email header fields (see documentation), some of which are retained/transferred by the email client when user replies, and these are used in authenticating, and processing the messages and sending on to the Notification URL where valid.
When you send your transactional emails, you add context information, which would will use to check on receiving the reply notification. This is information as well as the Account No is "signed" through cryptographic hash system using your private credentials, This is the same method that service will use to authenticate the non hashed part against the hashed part. Although that context data is meaningless to the service, it can verify it is correct and linked to the account. When receiving the reply you will repeat the process, then you will use the context information to process the message.
HTTP stands for Hyper Text Transfer Protocol the main protocol for transferring information across the Internet. HTTP POST stand for a specification for the protocol intended for sending information to a web resource to processed and or stored by that resource. Form more information: http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol
URL stands for Uniform Resource Locator. A reference to a web resource. In this case it refers to a full URI (Uniform Resource Identifier) and described by: http://www.ietf.org/rfc/rfc3986.txt