Emails can land in the spam folder due to various factors related to sender reputation, email content, authentication, list hygiene, and user engagement. Some users reported Really Good Emails landing in their spam folders, while others received them in their inbox, indicating that the issue may not be universal. Key factors influencing deliverability include sender reputation, authentication (SPF, DKIM, DMARC), email list hygiene (cleaning out inactive or invalid addresses), engagement (open and click rates), spam trigger words, and the ratio of images to text. Best practices involve warming up your IP, obtaining consent, segmenting lists, avoiding spam triggers, personalizing content, and providing a clear unsubscribe process.