The consensus from experts, marketers, and documentation is that Gmail considers both domain and IP reputation for email deliverability, though domain reputation is increasingly prioritized, especially with proper authentication (SPF, DKIM, DMARC). IP warming is crucial for new IPs to establish a positive sender reputation by gradually increasing sending volume, starting with engaged subscribers while carefully monitoring deliverability metrics. Sender reputation, assessed by ISPs based on sending behavior, directly affects inbox placement. Maintaining consistent sending practices, implementing email authentication protocols, and practicing list hygiene are critical for optimizing deliverability and protecting against spam filters and email-based attacks.