Email Industry Glossary
Definitions of essential email development, design, deliverability, and infrastructure terms.
Key Takeaways
- Essential email terminology explained in plain English.
- Covers technical standards (MJML, VML, MSO, Handlebars).
- Covers deliverability fundamentals (SPF, DKIM, DMARC, ESP).
Glossary of Terms#
ESP (Email Service Provider)
A company or cloud infrastructure service (like SendGrid, Mailchimp, or Postmark) that manages high-volume email transmission, reputation, IP warm-ups, and deliverability. PostBrix is an email builder, not an ESP.
MJML (Mailjet Markup Language)
An open-source, semantic XML markup language designed to simplify email development. MJML automatically compiles into responsive, email-client-tested HTML.
MSO (Microsoft Office)
Conditional comments (like <!--[if mso]>) recognized specifically by Microsoft Outlook desktop on Windows, which uses the Microsoft Word rendering engine.
VML (Vector Markup Language)
An XML-based vector graphic format supported by Microsoft Office. In email development, VML is used to render rounded buttons, drop shadows, and background images in Outlook desktop.
Preheader (Preview Text)
The snippet of text displayed next to or below the subject line in an email client's inbox view.
Merge Tag / Variable
A placeholder token (like {{firstName}} or *|FNAME|*) that is replaced with recipient-specific data at send time.
Deliverability
The measure of how successfully sent emails reach the recipient's primary inbox rather than bouncing or landing in the spam folder.
DKIM (DomainKeys Identified Mail)
An email authentication method using cryptographic signatures to verify that an email was actually sent by the domain owner and not altered in transit.
SPF (Sender Policy Framework)
A DNS record specifying which mail servers are authorized to send email on behalf of your domain.
DMARC (Domain-based Message Authentication, Reporting, and Conformance)
An email authentication policy protocol that tells receivers how to handle emails that fail SPF or DKIM checks (e.g. none, quarantine, or reject).
BIMI (Brand Indicators for Message Identification)
An email specification allowing organizations that authenticate via DMARC to display their verified brand logo next to incoming emails in supported inboxes.
Apple Mail Privacy Protection (MPP)
A privacy feature in iOS 15+ that pre-downloads remote images through proxy servers, resulting in artificial 100% open rate records for Apple Mail users.
Common Acronyms Quick Reference#
- AST: Abstract Syntax Tree (the internal JSON representation of an email).
- CTR: Click-Through Rate.
- CTA: Call to Action (primary button or link).
- CAN-SPAM: Controlling the Assault of Non-Slicked Pornography And Marketing Act.
- GDPR: General Data Protection Regulation.
- CASL: Canada’s Anti-Spam Legislation.
Frequently Asked Questions
Why do so many email development terms reference Microsoft Office?
Because Microsoft Outlook for Windows (2007 through 2021) uses Microsoft Word as its HTML engine rather than Internet Explorer or Edge, creating unique legacy requirements like VML and MSO conditional comments.
Does DMARC compliance affect template design?
DMARC affects server domain authentication, but having valid physical postal addresses and working unsubscribe links in your template footer is required for compliance alongside DMARC.