How to Build an SMS Service

Using Email to SMS Gateways

Because most U.S. carriers and many international carriers will convert emails to SMS messages and forward them on to their customers, email to SMS gateways present a highly accessible means of rapidly prototyping SMS services. However, in most cases they are not scalable solutions for a full-fledged service, because the carriers may arbitrarily block messages being sent from a particular service when volume reaches a certain point (perhaps as few as 50 messages in a day).

The Basics

Every major U.S. carrier and most international carriers provide a gateway to the Internet so that their customers can receive SMS messages sent via email. The sender addresses the message to an email address of the form ###########@carrier-sms-domain.com, it is converted by the carrier into an SMS and delivered. There are several lists online with the carrier to domain name mappings, including one at http://www.notepage.net/smtp.htm.

Who sent it?

One thing you'll learn quickly is that there is very little that is "standard" whe using email to SMS gateways. Each carrier has a few idiosyncrasies in how they send and receive messages. For example, while most carriers will fill in the From address with the phone number plus their domain (e.g., [e-mail]), a few don't. Verizon PCS, for example, allows its users to substitute a handle instead of the number, so a message sent to a Verizon PCS user with the address [e-mail]" might be replied to with a From address ...