High levels of user inactivity can have several negative impacts on your email marketing efforts. Firstly, it can lower your overall engagement rates, making it difficult to measure the success of your campaigns. Secondly, it can affect your sender reputation, as ISPs (Internet Service Providers) may interpret a lack of engagement as a sign of spammy behavior, potentially leading to your emails being sent to the spam folder. Finally, it can result in wasted resources, both in terms of time and money, as you're essentially sending emails to people who are not interested.