You want to count the amount of newsletters you received from the websites? I would never recommend to use an e-mail client and look up the amount manually.
A better solutions would be to use / register a domain and set up your own e-mailserver on a (virtual) server. For example, use Postfix. With Postfix you can create a pipeline to a script. In that script you could make a counter for every e-mailalias received. If you are familiar with Perl (or similar) it's quite easy to set up. Just follow a tutorial for setting up postfix with spamassasin, but replace spamassasin with your own daemon :) Ofcourse you can also outsource this with freelancer.com.
Just my suggestion.