What is the JICMAIL household sample size?

Over each quarter JICMAIL is tracking the mail activity of 1,000 households. 

Panellists record the mail they receive for a week and subsequent mail actions taken by them, or anyone in their household, for three more weeks. They then begin this process again with mail they receive the following week. Our panel is split into four groups, each starting on a different week meaning that we are tracking mail activity for every week of the year.