The email design glossary

Plain-English definitions for the terms that come up in email projects. Bookmark it for your next agency call.

Design terms

• Preheader — the preview text shown after the subject line in the inbox list; written deliberately, it's a second subject line.
• Hero — the first full-width visual block of an email.
• Module — a reusable content block (product grid, testimonial, CTA band) within a template system.
• Master template — a locked base template whose modules your team rearranges per send.
• Dark mode — inbox colour inversion; requires deliberate design and code to keep brands intact.

Development terms

• Table-based HTML — layout built with HTML tables, still the only reliably rendered structure in email.
• Fluid-hybrid — a responsive coding method that works even where media queries aren't supported.
• MSO conditionals — code comments targeting Microsoft Outlook specifically.
• VML — Vector Markup Language; how backgrounds and rounded buttons are drawn in Outlook.
• AMP for Email — Google's format for interactive, live-content emails.
• ESP — Email Service Provider: Klaviyo, Mailchimp, Omnisend, HubSpot.

Testing terms

• Render testing — previewing an email across real clients/devices before sending (we test 60+).
• Gmail clipping — Gmail truncates emails over ~102KB; kept in check by disciplined code.
• Seed list — test addresses across providers used to verify real-world delivery.

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