Block Type & Email Client Support Reference
Complete catalog of all visual and logic block types supported by PostBrix, their valid attributes, and detailed client compatibility matrix.
Key Takeaways
- Comprehensive compatibility matrix detailing which email clients support each PostBrix builder block.
- Core layout and content blocks (Section, Column, Text, Image, Button, Divider, Spacer, QR Code) enjoy 100% universal support across all inboxes.
- Interactive blocks (Accordion, Carousel, Navbar) leverage graceful degradation: expanding to vertical stacks on Outlook desktop and Gmail.
- VML vector graphics ensure background images and rounded buttons render cleanly in Microsoft Outlook desktop.
Complete Block Catalog & Specifications#
Master Block & Email Client Support Matrix#
Compare how each PostBrix block renders across the primary email client engines:
Graceful Degradation Mechanics#
When a client lacks support for interactive CSS features (like the CSS checkbox hack used by Accordions and Carousels):
- Accordion Degradation: On Outlook desktop and Gmail, all accordion panes are automatically rendered in an expanded state. The user sees all question titles and answer paragraphs stacked sequentially, ensuring zero content is obscured or inaccessible.
- Carousel Degradation: In clients without radio input CSS support, the carousel displays only the primary hero image with thumbnail anchors below, preserving visual appeal without broken interactive controls.
- Countdown Timer Degradation: On Windows Outlook desktop (Word engine), animated multi-frame GIFs display their first frame. PostBrix's timer engine generates the first frame with the exact remaining hours, minutes, and seconds at the instant of delivery, preserving urgency without broken visuals.
- Video Degradation: Native HTML5
<video>embeds are blocked by over 80% of email clients due to security sandboxing. PostBrix compiles video blocks into high-definition thumbnail images with centered vector play icons that link directly to your hosted video player. - Navbar Degradation: In clients that strip interactive hamburger checkboxes, the navigation bar cleanly displays standard inline text links.
Frequently Asked Questions
Will an interactive Accordion or Carousel break in Microsoft Outlook?
No. PostBrix compiles MJML with conditional comments (<!--[if mso]>) that gracefully display a static, expanded fallback in Outlook. Users see all content clearly with no broken UI elements.
Why do buttons render as rectangles in Outlook 2016–2021 desktop?
Outlook desktop uses Microsoft Word as its HTML engine, which does not support CSS border-radius. PostBrix wraps buttons in VML to guarantee 100% surface clickability and brand colors, displaying clean square corners in Outlook.
How do countdown timers behave when opened multiple times?
PostBrix countdown GIFs are served with short-duration cache headers. When a subscriber re-opens the email hours later, their email client fetches a refreshed GIF reflecting the newly calculated remaining time.
Are QR code blocks safe to send to enterprise recipients?
Yes. PostBrix QR codes are rendered as static, optimized PNG images served from SSL CDNs, which are 100% supported across all email clients including desktop Outlook.