Send a message to the given user.
@param user the user that should receive the message (must not be {@code null})
@param destination the destination to send the message to (must not be {@code null})
@param payload the payload to send (may be {@code null})
@param postProcessor a postProcessor to post-process or modify the created message
Send a message to the given user. @param user the user that should receive the message (must not be {@code null}) @param destination the destination to send the message to (must not be {@code null}) @param payload the payload to send (may be {@code null}) @param postProcessor a postProcessor to post-process or modify the created message