Improving IP warmup with AT&T and resolving low open rates involves a multi-faceted approach. Key strategies include maintaining consistent sending volume, segmenting email lists based on engagement (particularly for AT&T subscribers), validating subscriber lists to remove invalid addresses, and implementing proper email authentication. Additionally, checking AT&T's specific guidelines, conducting inbox placement testing, and using postmaster loops are recommended. Addressing issues like missing suppression lists and focusing on engaging content are also crucial for optimizing deliverability and open rates.