The default._bimi TXT Record Format

To complete a Brand Indicators for Message Identification (BIMI) deployment, you publish a DNS TXT record. This record tells receiving mail servers where to retrieve your SVG logo and your Mark Certificate.

This article documents the required syntax, tags, and formatting rules for the BIMI TXT record [1].

The Hostname (Selector)

Publish the BIMI record as a TXT record in your domain's DNS zone. The hostname (the selector) must use the following format:

[selector]._bimi.[domain]

The default selector is default. For the domain example.com, publish the TXT record at the following hostname:

default._bimi.example.com

Note: The protocol supports custom selectors for subdomains or business units, but most deployments use the default selector. Mail clients query default._bimi when no other selector is specified in the message headers.

The Record Value Syntax

The TXT record value is a semicolon-separated list of tags, using the same structure as a DMARC record.

1. The Version Tag (v=)

This tag is required and must appear first. It identifies the protocol version. Syntax: v=BIMI1;

2. The Location Tag (l=)

This tag is required. It specifies the HTTPS URL where the mail client retrieves your W3C SVG Tiny P/S logo file. Syntax: l=https://example.com/logo.svg; Constraint: The URL must use HTTPS. HTTP URLs fail validation.

3. The Authority Tag (a=)

This tag is optional in the base specification but required in practice for logo display in Gmail and Apple Mail. It specifies the HTTPS URL where the mail client retrieves your Verified Mark Certificate (VMC) or Common Mark Certificate (CMC) in .pem format. Syntax: a=https://example.com/certificate.pem; Self-asserted fallback: For self-asserted deployments (supported only by Yahoo and AOL), include the tag with an empty value: a=;

Complete Record Examples

Example A: Certified deployment (Gmail and Apple Mail)

Use this format to display your logo in Gmail and Apple Mail and to receive the Gmail blue checkmark.

Type:  TXT

Host:  default._bimi
Value: v=BIMI1; l=https://example.com/logo.svg; a=https://example.com/cert.pem;

Example B: Self-asserted deployment (Yahoo only)

Use this format for testing or when targeting Yahoo Mail before you obtain a VMC.

Type:  TXT

Host:  default._bimi
Value: v=BIMI1; l=https://example.com/logo.svg; a=;

Common Syntax Errors

The following errors cause validation failures:

1. Missing semicolons. Separate every tag with a semicolon.
2. HTTP URLs. Both the l= and a= tags must reference https:// endpoints.
3. Invalid SVG files. The l= tag must reference a W3C SVG Tiny P/S file. Standard SVG, PNG, or JPG files cause the mail client to skip logo display without an error.
4. Omitted a= tag. For self-asserted records, include the a= tag with an empty value (a=;). Some parsers reject records that omit the tag entirely.

Automated Record Generation

Manual record construction introduces syntax errors. To generate the SVG file and the DNS TXT string from your domain parameters, use makeBIMI, which provides a one-click copy interface.

After you generate the record, deploy it to your DNS zone. If you require a VMC to populate the a= tag for Gmail compatibility, use a certificate brokerage such as veriBIMI to handle certificate provisioning.

References

[1] M. Blank, et al. "Brand Indicators for Message Identification (BIMI)." IETF Datatracker, RFC 9091, https://datatracker.ietf.org/doc/html/rfc9091