phonenumber@operator.com - How do they do it?

In this question, Codygman gave an answer that some oper开发者_如何学Goators offer a way to send an SMS by sending an email to phonenumber@operator.com. I am curious about the technical solution behind that. I doubt they have a mailbox for every phone number.

Is there anyone out there who has a clue how they do it?

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Email on the internet operates on the SMTP protocol. Standard MTAs (mail transport agents) will deliver messages to static mailboxes.

All the above solution requires is a custom MTA that instead of delivering to static mailboxes it interprets the username part of the address as a phone number and then pipes the request to an SMS gateway.

Certain mail software might be configurable enough such that this won't even require custom software and can be done with straight configuration.