The first thing to check is the email policy/limitations your ISP may have for mass emails. Many limit how many emails you can send out in a given time frame.
If you open up the Send Mail dialog, you'll find that there is an option named: "Multiple Emails, one for each record in the found set" With this option, you can pull up a list of records where each record stores the email address of one recipient and you can send them all the same email message by selecting this option.
They are probably aware of TechSoup
A Nonprofit’s Introduction to FileMaker Pro
RCC Donations is a FREE open FileMaker Pro 10 or 11 template based on Starting Point template
MailChimp allows a free account to send 12,000 html newsletters emails a month to a list of up to 2,000 subscribers