As email service providers (ESPs) enhance their spam filters, they are more stringent in identifying and filtering out emails that appear unsolicited or irrelevant. These advanced filters scrutinize various elements such as sender reputation, email content, and user engagement.

Furthermore, the competition in email marketing has intensified, leading to a higher volume of emails being sent, which, in turn, increases the chances of emails being flagged as spam. The more emails an individual user labels as spam, the more likely similar emails are to be automatically redirected to the spam folder.

Additionally, maintaining a trustworthy sender reputation is crucial. ESPs often rely on metrics like bounce rates, open rates, and user complaints to determine whether an email should be delivered to the inbox. If an email sender does not adhere to best practices for maintaining a clean email list and sending relevant content, their emails are more likely to be filtered out