Google's reputation system assesses senders based on factors like spam complaints and engagement. IP warming builds trust with ISPs through a gradual increase in email volume sent to engaged subscribers. Authentication (SPF, DKIM, DMARC), consistent sending practices, quality content, and list management are crucial for building and maintaining a positive reputation. Segmenting lists, monitoring deliverability metrics, and understanding your audience are key considerations for successful IP warming and improved email deliverability.