---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/sendgrid/glossary/openrelay#article
headline: Open relay
description: "*Internet Security*. An unsecured SMTP relay that routes email between domains."
url: https://www.twilio.com/docs/sendgrid/glossary/openrelay
inLanguage: en
dateModified: 2025-11-07T21:55:06.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# Open relay

*Internet Security*. An unsecured [Simple Mail Transfer Protocol (SMTP) relay][smtp-relay] that routes email between domains. Anyone on the internet to send email messages through this relay.

Never configure an [SMTP server][] in this way: spammers can exploit it. ISPs block open relays.

To learn more, see the Twilio [Email Infrastructure Guide][].

[Email Infrastructure Guide]: https://www.twilio.com/en-us/resource-center/the-email-infrastructure-guide-build-it-or-buy-it

[smtp-relay]: /docs/sendgrid/glossary/smtp-relay

[SMTP server]: /docs/sendgrid/glossary/smtp-server