📨 BIMI Extension & Gmail Requirements Guide

This document provides a focused overview of the BIMI Extension, Gmail-specific requirements, and common troubleshooting steps for ensuring successful logo display using BIMI (Brand Indicators for Message Identification).

🧩 What Is the BIMI Extension?

The BIMI Extension is a certificate extension used in Verified Mark Certificates (VMCs) to explicitly identify them as intended for BIMI.

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Object Identifier (OID):1.3.6.1.4.1.57264.1.1
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Purpose:Signals to mailbox providers that the certificate is for BIMI use.
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Presence:Optional in the X.509 spec, but recommended, especially for Gmail.

Note: Absence of the BIMI Extension may not cause outright failure but could prevent logo display in Gmail.

📬 Gmail BIMI Requirements

To display your brand logo in Gmail inboxes, the following must be in place:

Component	Requirement	Notes
DMARC Policy	Required	Must be set to `quarantine` or `reject`.
Verified Mark Certificate	Required	Issued by DigiCert or Entrust.
BIMI Extension in VMC	Recommended	OID `1.3.6.1.4.1.57264.1.1` should be present.
State/Province Field	Required	Must be present in VMC Subject DN.
Street Address Field	Required	Must be present in VMC Subject DN for Gmail.
BIMI TXT Record	Required	Published at `default._bimi.<domain>` with `v=`, `l=`, and `a=` tags.
Logo File	Required	Must be SVG Tiny PS format, hosted via HTTPS.
Logo Dimensions	Required	Minimum 96x96 pixels, must be square (1:1 aspect ratio).
SVG ViewBox Format	Required	Must be space-delimited (e.g., "0 0 400 400"), not comma-delimited.

🛠️ Troubleshooting Gmail BIMI Failures

If your logo is not appearing in Gmail, check the following:

Missing State/Province Field

Gmail requires the ST field in the Subject DN of the certificate.
If omitted, Gmail will not display your BIMI logo.

BIMI Extension Not Found

May trigger a warning.
Contact your CA to re-issue the certificate with the BIMI extension OID.

Incorrect DMARC Policy

Must not be p=none.
Use p=quarantine or p=reject.

Logo Format or Hosting Issues

Must be SVG Tiny PS format.
Served over HTTPS, with proper MIME type (image/svg+xml).

DNS TXT Record Issues

Ensure TXT record is live and correctly formatted.
Example:

default._bimi.example.com. IN TXT "v=BIMI1; l=https://example.com/logo.svg; a=https://example.com/vmc.pem"

🎨 Google-Specific Logo Requirements

Gmail has specific requirements for BIMI logos to ensure proper display:

Size and Dimensions

Minimum size: 96x96 pixels (Gmail requirement)
Maximum size: 2048x2048 pixels
Aspect ratio: Must be perfectly square (1:1)
File size: Recommended under 32KB for optimal performance

SVG Format Requirements

ViewBox format: Must use spaces, not commas
✓ Correct: viewBox="0 0 400 400"
✗ Wrong: viewBox="0, 0, 400, 400"
Format: SVG Tiny PS (Portable/Secure) only
No embedded content: No JavaScript, raster images, or animations

Display Considerations

Gmail displays logos in circular avatar slots
Design your logo to look good when cropped to a circle
Avoid important details near the edges
Test your logo at small sizes (32x32 pixels) for readability

🔚 Final Notes

Gmail uses strict validation for BIMI.
Even if BIMI records pass external validators, logo display in Gmail depends on full compliance.
Use Gmail Postmaster tools for verification of your BIMI implementation.

Ensure your certificate includes the right fields and extensions for a seamless Gmail BIMI experience.

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