Frequently, applications need to react to some kind of event, they receive a message from a user or software and they need to act accordingly. The whole nature of networking-based applications lies in reacting to received messages, but a very specific and common case of this class of applications are applications that need to react to received emails.
The typical case is when a user needs to send some kind of document to your application (usually an ID card or signed contracts) and you want to react to that event, such as enabling the service once the user sent the signed contract.
This requires us to be able to access the received emails and scan through them to detect sender and content.
