If you notice your list members are marked On Hold or if you see a banner message at the top of the page letting you know that you've outgrown your contact limit, it's time to upgrade your account. On Hold contacts have been uploaded to your account, but cannot be mailed because you have exceeded the maximum number of email addresses from your pricing package.
To make these addresses mailable, you'll need to change your pricing package. Click the Upgrade button to make changes to your plan. For more information on upgrading, visit this page.