Transactional emails from SendGrid often land in spam while campaign emails reach the inbox due to a multifaceted combination of factors. These include poor IP reputation stemming from shared IPs or lack of proper IP warm-up, content characteristics that trigger spam filters, missing or incorrect header information, and sending volume patterns such as sudden bursts from new IPs. Authentication issues (SPF, DKIM, DMARC), higher spam rates, the absence of feedback loops, and a low sender reputation also contribute significantly. Furthermore, engagement metrics such as low open and click-through rates, the lack of a double opt-in strategy, poor email list hygiene, Gmail's sophisticated fingerprinting techniques, and individual inbox training through behaviors like deleting test emails without engagement play critical roles. Finally, different configurations applied by inbox providers can affect the emails.