Does BIMI use a specific DNS subdomain for its TXT record?

Brand Indicators for Message Identification, or BIMI, is an email standard that allows you to display your company's logo next to your messages in the recipient's inbox. It's a powerful way to increase brand recognition and trust. Like other email authentication standards such as SPF, DKIM, and DMARC, BIMI is implemented by publishing a specific type of record in your domain's DNS.

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Just like the SPF, DKIM, and DMARC protocols, a BIMI record is published on the DNS of your sending domain (or domains). That may be different from your main website domain if you use subdomains to send emails.

The core of your question is about where exactly this record lives. Does it need a special subdomain? The short answer is yes, it does.

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BIMI records are TXT records that are placed at a specific location within your DNS. The standard format requires a subdomain that follows a particular pattern: default._bimi.yourdomain.com. Let's break that down.

• yourdomain.com: This is the domain (or subdomain) you send email from.
• _bimi: This is a fixed part of the structure, indicating that this DNS record is for BIMI.
• default: This part is known as a "selector." While "default" is the most common one, you can use other selectors for different purposes.

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Publish a BIMI record for your domain in the control panel of your DNS host. You can add a TXT record for default._bimi.yourdomain.com with the value v=BIMI1;...

The selector is a crucial part of the BIMI specification. If you are familiar with DKIM, you'll recognize the concept. Selectors allow you to have multiple, distinct BIMI records for a single domain. Why would you want this? Large organizations might want to display different logos for emails coming from different departments or brands.

For example, you could have a record for marketing._bimi.yourdomain.com and another for support._bimi.yourdomain.com, each pointing to a different logo file. The receiving mail server finds the right logo by looking at the selector specified in the email's BIMI-Selector header. If no selector is specified in the header, it falls back to looking for the "default" record.

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A selector is used in concert with a domain name and a specific term to construct a DNS label, and a DNS TXT record is then queried at that location for a BIMI assertion record. The assertion record will contain, among other things, a URL that points to the logo that should be displayed.

You can also publish BIMI records for subdomains. For instance, if you send marketing emails from news.yourbrand.com, you can create a BIMI record specifically for it at default._bimi.news.yourbrand.com. This gives you granular control over your branding across different sending streams.

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You can also only publish a BIMI record on a subdomain if you don't want the organizational domain covered or if you want to restrict which mail streams get the BIMI treatment. You just need to have DMARC set up on your subdomain and have it set to an enforcement policy.

The receiving server will first check for a BIMI record on the specific subdomain from the email's From address. If it doesn't find one, it will then check the organizational or parent domain. This fallback mechanism ensures that you can set a default logo at the top level while using more specific ones on subdomains where needed.

So, to directly answer the question: yes, BIMI uses a specific DNS subdomain structure for its TXT record. The standard format is selector._bimi.yourdomain.com, where default is the most common selector. This structure provides a flexible and scalable way to manage your brand's logos across different domains and email streams, all controlled through simple DNS entries.