For immediate blanket communication to a pre-selected list, nothing currently beats an email blast. We strongly advise parishes to conduct these using an anti-spam compliant email service. Many parishes and other dioceses, we use Constant Contact. You can upload your addresses to it, slice and dice the lists any which way, create different templates to suit your different needs, and send as many emails as you want for a single monthly fee. Another highly recommended eNewsletter service is MailChimp. Other services can be found with the click of a mouse button on search engines such as Google.
Please note that it is, however, most unwise to place all your faith in emails: our experience suggests that an open rate of 30% is good for any message, even when of seemingly vital importance to the recipient.