Total Customers in Pocomos
The best place to find out how many active customers you have is on your Owner's Dashboard:
You can also go to customers->view all->scroll to the bottom and it will give you a total customer count
Customer Subsets
To find a subset of customers (for example, how many inactive customers or customers with a certain contract type), go to customers->advanced search and select the criteria you would like to search for, then scroll to the bottom and hit "search." Once you get your list of results, scroll to the bottom of the page and see the total count.
You can send emails to all of your customers or to subsets through the advanced search. Check out this article for instructions.