Thinking of implementing mass email to Drupal as you want to sent emails to your registered user? There are several options you could go with.
Simplenews newsletters, this would be most obvious choice as its most developed and has most options. It could be a overkill for your need but its mostly a safe bet. You can send real newsletters with it but you can also send messages plain or HTML, with or without attachment and have your users grouped by roles or just by subscriptions. Its all mostly good and you have cron settings and its well testes module which should work for you without problem.
Mass Contact is a module just for that, mass contacting, its no newsletter altough you can have your users categorized by category which are in fact roles you choose for each category so you can combine them. Subject, body and attachment, everything you need is there for emailing and also works without problem, some fine tuning is there also, nut much but its a good choice for sending mass messages. Take a note also that you can choose multiple categories when sending message, future that is still not implemented in Simplenews.
Views Mail this is module that depends on simplenews, it has its strong sides as it enables you to make views lists of users and fine tune this lists and then send emails. Problem is that it depends on simplenews so configuration is rather hard and not so much for regular users, if you are not programmer/administrator just skip this. Out of the box mail went through so mailing works.
Advanced user has similar fine tuning user list as above module, even a bit better as you can checkbox each users after you filtered your lists, this is what is really needed to have good list. Unfortunately mails didn't go through when testing latest 3.x DEV and there is attachment option missing when sending messages.
Views Send uses views and VBO module for lists and then you can execute bulk email action for email sending. Works fine and has fine tuning options as above module, as it's a view so you can do anything to sort your list. Doesnt have attachment option.