Spam Complaints: When recipients mark your emails as spam, it signals to email service providers (ESPs) that your emails are unwanted. High Bounce Rates: Sending emails to invalid addresses can lead to a high bounce rate, which negatively impacts your sender reputation. Irrelevant Content: Sending irrelevant or low-quality content can frustrate recipients, leading them to unsubscribe or mark your emails as spam. Non-compliance: Failing to adhere to regulations like the CAN-SPAM Act or GDPR can result in fines and damage to your brand's reputation. Inconsistent Sending Patterns: Irregular email sending can confuse recipients and ESPs, leading to lower engagement and deliverability issues.