def sum_stats(stats_data):
    """
    Summarize the bounces, complaints, delivery attempts and rejects from a
    list of datapoints.
    """
    t_bounces = 0
    t_complaints = 0
    t_delivery_attempts = 0
    t_rejects = 0
    for dp in stats_data:
        t_bounces += dp['Bounces']
        t_complaints += dp['Complaints']
        t_delivery_attempts += dp['DeliveryAttempts']
        t_rejects += dp['Rejects']

    return {
        'Bounces': t_bounces,
        'Complaints': t_complaints,
        'DeliveryAttempts': t_delivery_attempts,
        'Rejects': t_rejects,
    }