Plugins
Plugins exist to extend, or modify the behaviour of Swift Mailer. They respond to Events that are fired within the Transports during sending.
There are a number of Plugins provided as part of the base Swift Mailer package and they all follow a common interface to respond to Events fired within the library. Interfaces are provided to "listen" to each type of Event fired and to act as desired when a listened-to Event occurs.
Although several plugins are provided with Swift Mailer out-of-the-box, the Events system has been specifically designed to make it easy for experienced object-oriented developers to write their own plugins in order to achieve goals that may not be possible with the base library.