The impact of Sendgrid MTA retries on sender reputation is complex and multifaceted. While retries are a normal and expected part of email delivery, excessive or aggressive retries can negatively impact sender reputation. Several factors play a role, including deferral rates, engagement metrics, list hygiene, and authentication. Proper management of bounces, particularly hard bounces, is crucial, as is monitoring deferral rates to identify underlying issues like blacklisting. Authentication (SPF, DKIM, DMARC) and engagement (opens, clicks) can offset negative impacts, while feedback loops help address complaints and improve reputation.