Upgrade your list (increase the number of allowed subscribers)
If the number of subscribers on your list exceeds the permitted number an "Upgrade now" link will appear in your Account.
When the permitted number has been exceeded by more than 10%, automated notices are emailed to list owners each day. You can then either upgrade the list or remove the excess subscribers.
When upgrading, the payment due is calculated from the "remaining time" at the new rate. After 7 days of notices if the list is still oversubscribed it is suspended.