To keep your emails safe, and to guard our reputation as a Good Email Server, we limit the number emails you can send in an hour to 100.

We all get spam.

If you are sending out a newsletter, a flyer, a business advertisement, even party invitations or a school letter, then sending it by email is a very bad idea.
Doing any of these things will make your domain look like a spammer, and may cause legitimate emails from you in the next day or so get sent straight to spam at the recipients end.
Using BCC, while it was once a good idea, now ups your rate of being seen as spammer.
Using HTML in an email ups your rate of being seen as spammer.
Embedding pictures ups your rate of being seen as spammer.
Embedding a PDF ups your rate of being seen as spammer.

In today's age of emails, if you are sending the same email to more than ten people then you really should be using an email service to make sure your emails get through the various spam filers that exist out there.
I suggest that you use Mail Chimp.

http://mailchimp.com/