What Are Invalid Email Addresses?
Invalid email addresses occur when the recipient's email address is misspelled, no longer exists, or is otherwise incorrect. Regularly cleaning your 
email list to remove such addresses can significantly reduce rejection rates.
How Do Spam Filters Work?
Spam filters analyze incoming emails based on various criteria to determine if they are spam. Factors such as 
poor email content, excessive use of promotional language, and suspicious links can trigger these filters. To avoid spam filters, ensure your email content is relevant and valuable to the recipient.
How to Handle Bounced Emails?
Bounced emails are those that couldn't be delivered to the recipient's inbox. There are two types: soft bounces (temporary issues) and hard bounces (permanent issues). Monitoring bounced emails and taking corrective action, such as updating or removing invalid addresses, is essential for maintaining a healthy email list.
    Regularly 
clean your email list    Use a double opt-in process to verify email addresses
    Craft high-quality, relevant email content
    Avoid spammy language and excessive links
    Monitor your 
sender reputation    Use a reliable 
ESPWhat Are Feedback Loops?
Feedback loops are mechanisms provided by ISPs to report spam complaints. Monitoring these feedback loops allows you to identify and address issues causing recipients to mark your emails as spam, thereby reducing future rejections.
Conclusion
Understanding the reasons behind email rejection and implementing best practices can significantly enhance your email marketing effectiveness. Regularly clean your email list, create high-quality content, and use email authentication to improve deliverability and minimize rejections.