A drop in Sender Score can stem from several interconnected factors, often reflecting underlying deliverability issues. Poor list hygiene, characterized by high bounce rates, spam complaints, sending to spam traps, or acquiring lists from compromised or low-quality sources, significantly impacts Sender Score. Being blacklisted and experiencing sudden spikes in sending volume are also major contributors. Technical aspects like inadequate email authentication (SPF, DKIM, DMARC) and inconsistent sending patterns further erode sender reputation. Engagement metrics, particularly low open rates, serve as indicators of deliverability problems. Shared IP addresses, where the actions of other senders influence your score, add another layer of complexity. Addressing a low Sender Score involves improving list hygiene, warming up new IPs, authenticating emails, ensuring consistent sending practices, delivering valuable content, actively engaging subscribers, monitoring sender reputation using tools like Google Postmaster Tools, investigating recent campaigns for deliverability issues, and optimizing sending infrastructure. Focusing on actual deliverability problems and doing root cause analysis is also considered a good practice, instead of solely focusing on the sender score metric as an absolute value.