In the past you could send a mass email to a few hundred people using your email client programs such as Outlook, etc… but this is not a good option anymore as companies like Comcast, Google, and AOL have setup tougher measures to catch spam. If you send the email out with your local email client, your message is sent out as fast as possible… and this rate of sending is what gets your e-mail address and IP address in trouble and prevents your e-mails from reaching your customers inboxes.  Even if they are subscribed to your newsletter!  To avoid this kind of issue I suggest using a company like SMTP.com (  $5 per month  ) . They provide you with custom SMTP sending credentials that you enter into your email client send settings.  They will not send the messages nearly as quickly and this will keep your IP address and e-mail account in good standing.