AT&T's email blocking issues stem from a combination of factors, including a major outage, stricter filtering practices, poor sender reputation, authentication failures, and inadequate list hygiene. AT&T uses distinct filtering methods and may be more aggressive than other ISPs. Solutions involve addressing the outage, improving email authentication (SPF, DKIM, DMARC), monitoring and acting on feedback loops and bounce rates, proper IP warming, maintaining valid rDNS records, practicing good list hygiene, monitoring data quality, and segmenting sending. Data quality and how that data is actioned is very important for keeping engagement metrics up. Correct authentication and reputation management are critical, as blocks often occur despite seemingly correct configurations.