Swift Mailer TODO List
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  * Add an eventCancelled property and setEventCancelled() method all events
  * Merge Swift_Connection and Swift_ConnectionBase
  * Create a SignedMessage class using openssl_pcks7_sign()
  * Add VERP functionality, probably via plugin
  * Possibly make ConnectionRotator/Multi deal with failied connections during the
    send process - again, for batch mailing. Currently these connections only check
    for failures at connection time.