The first part of a 5-part series on message deliverability discusses how carriers evaluate messages. When you hit send, your SMS is translated into data and sent across an elaborate web of interconnected carrier networks. As it travels, the message is checked for SPAM by various checkpoints that may differ by carrier and can be subject to change at any time. Criteria considered include the sender's reputation, messaging type, volume, and content. Keeping these criteria in mind increases the chances of successful delivery.