---
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"@type": TechArticle
"@id": https://www.twilio.com/docs/sendgrid/glossary/system-fields#article
headline: Reserved substitution tags
description: "*Configuration*. Placeholder labels that get replaced with personalized content in an email campaign."
url: https://www.twilio.com/docs/sendgrid/glossary/system-fields
inLanguage: en
dateModified: 2025-11-07T21:55:06.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# Reserved substitution tags

*Configuration*. Placeholder labels that get replaced with personalized content in an email campaign.

Though an email campaign can use placeholders based on any [custom][] or [reserved] field, Twilio makes these tags available to any email campaign.

The Design & Code editor guide includes the [full list of reserved substitution tags][subtags].

[subtags]: /docs/sendgrid/ui/sending-email/editor#reserved-substitution-tags

[custom]: /docs/sendgrid/glossary/custom-fields

[reserved]: /docs/sendgrid/glossary/reserved-fields