The choice of email tool has a multifaceted impact on email deliverability. Subtle differences exist between tools in terms of IP reputation and traffic patterns, while statistical anomalies can cause varied delivery rates even within the same ESP. Crucially, sender reputation—influenced by IP/domain reputation and adherence to authentication protocols (SPF, DKIM, DMARC)—determines inbox placement. Shared IPs carry the risk of others' poor sending practices affecting your deliverability. Following guidelines from major providers like Gmail and Outlook, warming up IPs, maintaining list hygiene, avoiding spammy content, and leveraging dedicated IPs offer control over reputation. Feedback loops help identify and rectify spam complaints. Tools with anti-harvesting policies protect deliverability. Finally, selecting a reputable tool is paramount, as a poor reputation directly damages your sending capabilities.