The presence of non-existent or inactive addresses can significantly reduce your domain reputation, lead to your emails being marked as spam, and stop campaigns.
If your email address database was collected manually, for example, from offline forms or registration forms, there is a high probability of typos. Even one error in an address can make it invalid.
For final quality checking of your database, it is recommended to use special services — email validators. They will help you identify not only typos but also deactivated or blocked addresses.
Over time, part of your audience may become inactive. This can happen for various reasons: users changed addresses, lost interest in your campaigns, or simply do not open your emails. In some services, if a user has not accessed their mailbox for a long time — it is deleted and sending to such an address will result in an error. To prevent non-existent addresses from spoiling statistics and reducing sender reputation, it is important to regularly check and clean your database.