Emailing engaged email addresses is important for several reasons:

Higher deliverability rates:
Email service providers (ESPs) use engagement metrics, such as open and click-through rates, to determine whether emails are being sent to the inbox or the spam folder. When you send emails to engaged email addresses, you are more likely to receive higher engagement rates, which can improve your sender reputation and increase the likelihood that your emails will be delivered to the inbox.

Improved sender reputation:
When you send emails to unengaged email addresses, your emails are more likely to be marked as spam. This can harm your sender reputation and lead to lower deliverability rates for all of your emails, even to engaged email addresses.

Cost savings:
Emailing unengaged email addresses can increase your email marketing costs by using up valuable resources, such as sending credits, that could be better spent on engaging subscribers who are more likely to convert.

Better results:
Engaged email addresses are more likely to convert into paying customers or take the desired action, such as signing up for a newsletter, making a purchase, or registering for an event. By focusing on engaged email addresses, you can improve your overall email marketing results and maximize the return on investment for your email marketing campaigns.

Overall, focusing on engaged email addresses is a best practice for email marketers, as it can lead to higher deliverability rates, improved sender reputation, cost savings, and better overall results.