A bad IP reputation and the appearance of unknown IPs can severely harm e-commerce email deliverability, leading to emails being marked as spam or rejected. This often stems from issues like SPF record misconfigurations, domain spoofing, compromised accounts, poor list hygiene, and shared IP risks. Implementing SPF, DKIM, and DMARC is critical, along with monitoring DMARC reports and IP reputation using tools like Google Postmaster Tools and Microsoft SRD. Regularly cleaning email lists, monitoring blocklists, and securing email servers are also essential. Proactive measures, such as subscribing to feedback loops and testing deliverability, help maintain a positive sender reputation and minimize negative impacts. Avoid adding TXT records to Sendgrid subdomains and be aware of potential over-complication of SPF records.