You can send no more than 14 emails per minute and e-mail message size limit is 5MB.
Mass or newsletter mailing is not allowed.
All email sending count toward mass mail, even approving comment, announcement or notification, private messaging, etc or have a contact form on your site even the email is just sending to you.
If you don't disable email sending, your site will get suspended as quickly as your account un-suspend.
To avoid this limitation, you need to upgrade to paid hosting.