What is the role of the 'a=' tag in a BIMI record?
Matthew Whittaker
Co-founder & CTO, Suped
Published 23 Nov 2024
Updated 1 Oct 2025
9 min read
When you open your inbox, you likely see brand logos next to emails from trusted senders. This visual cue is often powered by Brand Indicators for Message Identification (BIMI), an email standard that allows organizations to display their trademarked logos in the recipient's inbox. BIMI works by linking your verified brand logo to your authenticated email domain, providing an immediate visual signal of trust to your recipients. But how does this logo verification actually happen? This is where the 'a=' tag in your BIMI record comes into play.
The 'a=' tag serves a very specific and critical function within a BIMI DNS TXT record. It points to the location of your Verified Mark Certificate (VMC), which is a digital certificate that confirms your ownership of the logo you wish to display. Without this certificate, the 'a=' tag would have no validated logo to reference, limiting the trust and visibility benefits that BIMI offers. Essentially, it's the digital handshake that connects your brand's visual identity to its authenticated email sending practices.
Understanding the 'a=' tag is key to fully leveraging BIMI for brand protection and engagement. It transforms a simple logo display into a strong indicator of email authenticity, helping your emails stand out and instill confidence in your audience. This process is deeply rooted in strong email authentication, particularly DMARC enforcement, which dictates how recipient email servers should handle unauthenticated messages.
The 'a=' tag: verified mark certificate (VMC) validation
Understanding BIMI and its core components
BIMI is a relatively new standard designed to enhance the visual appeal and trust of emails. It works by ensuring that the sender has properly authenticated their emails using DMARC, SPF, and DKIM. Once these authentication protocols are in place and your DMARC policy is set to quarantine or reject, BIMI allows you to publish a DNS TXT record that points to your brand's logo. This logo then appears in supported email clients, making your emails instantly recognizable.
A BIMI record is composed of several tags, each with a specific role. For instance, the 'v=' tag specifies the BIMI version, typically BIMI1. The 'l=' tag points to the SVG file of your logo, which must meet specific requirements for display. Then there's the 'a=' tag, which is the focus here. It introduces an additional layer of verification that significantly boosts the security and trustworthiness of your brand's visual presence in the inbox.
While displaying a logo itself offers visual benefits, the 'a=' tag ensures that logo is officially recognized and authenticated by a trusted third party. This distinction is crucial in an era where phishing and brand impersonation are rampant. By requiring a verified certificate, the 'a=' tag makes it much harder for malicious actors to spoof your brand's logo, providing a stronger defense against email fraud and enhancing consumer confidence.
The 'a=' tag: Verified Mark Certificate (VMC) validation
The 'a=' tag explained: VMC validation
The primary role of the 'a=' tag in a BIMI record is to specify the URL of your Verified Mark Certificate (VMC). A VMC is a digital certificate issued by a Certificate Authority (CA) that authenticates your ownership of a registered trademark logo. This certificate is vital for demonstrating that your brand's logo is legitimate and that your organization has the right to use it. When an email server receives an email from your domain, it looks up your BIMI record. If an 'a=' tag is present, it will then retrieve the VMC from the specified URL to verify the logo's authenticity.
This validation process is a cornerstone of BIMI's security benefits. By requiring a VMC, the 'a=' tag ensures that only legitimate, trademark-holding organizations can display their logos. This prevents unauthorized entities from using your brand's logo to deceive recipients. The VMC acts as a trusted third-party endorsement, giving email clients and recipients a higher degree of confidence that the sender is who they claim to be.
Implementing a BIMI record with an 'a=' tag (and thus a VMC) elevates your email security posture significantly. It moves beyond just displaying a logo, embedding verifiable trust into your email communications. For businesses serious about brand integrity and protecting their customers from phishing, incorporating a VMC via the 'a=' tag is an essential step. It's a crucial differentiator between simply having a logo and having a verified logo in the inbox.
The structure and types of BIMI records
The structure and types of BIMI records
A typical BIMI record is a TXT record added to your DNS, often found at a subdomain like default._bimi.yourdomain.com. The 'a=' tag's value is a URL pointing to your VMC file, usually hosted on your web server. Here's what a complete BIMI record with an 'a=' tag might look like:
BIMI DNS TXT Record ExampleDNS
default._bimi IN TXT "v=BIMI1;l=https://www.yourdomain.com/path/to/logo.svg;a=https://www.yourdomain.com/path/to/vmc.pem;"
There are two main approaches to BIMI implementation: using a self-signed BIMI record (without an 'a=' tag) or leveraging a Verified Mark Certificate (VMC) with the 'a=' tag. While self-signed BIMI is simpler to implement, it offers a lower level of assurance, and fewer email clients support logo display without a VMC. The 'a=' tag signals to recipient servers that your logo has been rigorously validated, unlocking broader support and higher trust with email providers. You can find accredited certificate providers on the BIMI Group's website.
Benefits of using the 'a=' tag with VMCs
Benefits of using the 'a=' tag with VMCs
The decision to include the 'a=' tag and use a VMC brings several significant benefits to your email marketing and security efforts. Firstly, it provides enhanced brand recognition and recall. Your logo, visibly authenticated, helps your emails stand out in a crowded inbox, making them easier for recipients to spot and increasing the likelihood of engagement. This is especially valuable for brands looking to reinforce their identity across all touchpoints.
Without the 'a=' tag (Self-Signed)
Trust level: Lower, as there's no third-party verification of logo ownership.
Client support: Limited, some email providers may not display the logo.
Security: Primarily relies on DMARC, less protection against logo impersonation.
With the 'a=' tag (VMC)
Trust level: High, as logo ownership is verified by a Certificate Authority.
Client support: Widely supported by major email clients, including Google and Yahoo.
Security: Stronger defense against phishing and brand impersonation.
Secondly, the 'a=' tag contributes to significantly improved trust and legitimacy for your email communications. When recipients see your familiar logo with an added layer of verification, they are more likely to open and interact with your messages, knowing they are from a legitimate source. This increased trust can translate directly into higher open rates, click-through rates, and ultimately, better campaign performance.
Lastly, the 'a=' tag provides a powerful defense against phishing and brand impersonation. Because a VMC proves legitimate ownership of the logo, it becomes much harder for cybercriminals to create convincing fake emails using your brand's visual identity. This added layer of security protects both your brand's reputation and your customers from potential scams. For BIMI to work effectively with VMCs, your domain must have a DMARC policy set to enforcement (p=quarantine or p=reject).
Implementing and monitoring BIMI with the 'a=' tag
Implementing and monitoring BIMI with the 'a=' tag
Successfully implementing BIMI with the 'a=' tag involves a few key steps. First, ensure your email authentication, particularly DMARC, is fully configured and enforced. This means your DMARC record is at a policy of 'quarantine' or 'reject'. Next, you'll need to obtain a Verified Mark Certificate (VMC) from an authorized Certificate Authority. Once you have your VMC and your BIMI-compliant SVG logo, you'll host these files on your web server and then update your BIMI DNS TXT record to include both the 'l=' tag (for your SVG logo) and the 'a=' tag (for your VMC).
Don't forget DMARC!
BIMI strictly requires a DMARC policy of p=quarantine or p=reject to function. Without this strong enforcement policy, email clients will not display your BIMI logo, even if your 'a=' tag and VMC are perfectly configured. Ensure your DMARC is ready before pursuing BIMI.
After deployment, continuous monitoring is essential. Tools like Suped provide a unified platform for DMARC, SPF, DKIM monitoring, alongside blocklist monitoring and deliverability insights. Suped's AI-powered recommendations can help you ensure your BIMI record, including the 'a=' tag, is correctly configured and working as intended, providing real-time alerts if any issues arise. This proactive approach helps maintain your brand's strong visual presence and protect your email integrity.
Conclusion
Conclusion
The 'a=' tag in a BIMI record is far more than just another technical detail, it is a cornerstone of advanced email security and brand identity. By pointing to a Verified Mark Certificate (VMC), it provides irrefutable proof of your brand's logo ownership, fostering deep trust with recipients and fortifying your defenses against phishing attacks. This level of verification is essential in today's digital landscape, where email remains a primary vector for communication and cybercrime.
Embracing BIMI with a VMC, facilitated by the 'a=' tag, demonstrates a commitment to email best practices and a proactive stance on brand protection. It not only enhances your email's visual impact but also significantly boosts its perceived legitimacy. As email clients increasingly prioritize verified senders, a properly configured BIMI record with the 'a=' tag will be a key factor in ensuring your messages reach the inbox, resonate with your audience, and remain secure.
Google and 
Yahoo.
