Why is the email "unreachable"?
When you send newsletters or individual emails to your site's audience contacts, we'll check if your recipient's email is valid and reachable before sending. The purpose of this is to increase your successful delivery rate and sender reputation, which helps to ensure your emails are not marked as spam by recipients in the future.
In your Audience List, you may see contacts who are marked as "unreachable". This means their email is incorrect, dummy, fake or temporary. You will not be able to send emails or newsletters to unreachable email addresses.
What can I do?
If the email address is wrong (e.g. due to a typo upon submission) and you know the correct address, you can manually import the correct email as a new contact and delete the unreachable email contact.
If you don't need to contact this person, then you don't have to worry about anything.