The system will let you exceed your limit up to the limit of the next mailing list level.   For example, if you are on the Level 1 plan of 10,000 emails per month you are allowed to go up to the Level 2 limit of 20,000 emails per month before the system will stop a mailing from being sent.

If you go over your plan limit (10,000 emails in the example above), you will be charged overages based on the number of emails you sent over your plan limit. You may upgrade your plan at any time.

For details on the plan levels and overage rate please see this page:

http://www.lexiconn.com/services/mailing_list.html