If you are using the Export utility and notice is not pulling the entire email list, it usually has to do with the service checkboxes.
Click on File, Export.
The checkboxes for Groom, Board, Daycare, etc. pull from the labels on the pet's card. For example, if you check the box for Board and the pet does not have Board highlighted on his pet card, he will not be included in the export.
Unless you are certain you checked the options for all pets, leave the checkboxes blank on the utility and it will pull your entire email list.