What are 'undisclosed recipients' in email and when should they be used?
Matthew Whittaker
Co-founder & CTO, Suped
Published 13 Nov 2025
Updated 13 Nov 2025
9 min read
The term 'undisclosed recipients' in an email can often cause confusion, especially for those new to email management or dealing with legacy systems. It typically appears in the 'To:' field of an email when the actual recipients have been added to the Blind Carbon Copy (BCC) field, and no one is explicitly listed in the 'To:' or 'CC:' fields. This practice dates back to earlier email standards, serving as a workaround to ensure the email headers were syntactically correct when explicit recipients were intentionally hidden.
While the intention behind using undisclosed recipients is usually to protect the privacy of a large group of email addresses, its implementation can have significant implications for email deliverability and sender reputation in today's sophisticated email ecosystem. Many modern email clients and spam filters view this practice with suspicion, potentially impacting whether your messages reach the inbox or end up in the spam folder. Understanding the nuances of this old practice is crucial for anyone managing email communications.
I've encountered this question frequently, especially from users transitioning from older email habits or integrated systems with outdated email functionalities. Let's delve into what 'undisclosed recipients' truly signifies and explore when, if ever, it might still be considered for use.
Modern approaches to email sending
How 'undisclosed recipients' works
At its core, 'undisclosed recipients' is a convention, not a distinct email address or feature. When you send an email and place all the recipients in the BCC (Blind Carbon Copy) field without listing anyone in the 'To:' or 'CC:' fields, most email clients and servers will automatically substitute 'undisclosed recipients' in the 'To:' display. This ensures that the email conforms to the expected header structure, even though no specific recipient is publicly addressed.
The primary purpose is to keep recipient addresses private from one another. Each recipient receives the email, but they only see 'undisclosed recipients' in the 'To:' field and are unaware of who else received the message. This can be useful for certain types of communications where privacy is paramount, such as sending updates to a large contact list that shouldn't know each other's email addresses. The RFC 5322 standard, which governs email message format, allows for such scenarios, although it doesn't explicitly define 'undisclosed recipients' as a specific address.
While it technically achieves its goal of hiding addresses, this method is largely a relic from an earlier era of email. Modern email practices, especially for bulk sending and marketing, have evolved significantly, offering more robust and deliverability-friendly ways to manage recipient privacy. Relying solely on the BCC field with an empty 'To:' can inadvertently trigger spam filters, which look for signs of legitimate email sending behavior. How does using only BCC affect deliverability? It's generally not recommended for professional communications.
When to consider using it (and its limitations)
The primary situation where 'undisclosed recipients' might be considered is for ad-hoc, small-scale communications where you need to send an email to a group of people who don't know each other, and you want to protect their privacy by not revealing their email addresses. For example, inviting a diverse group of contacts to an event where you don't want to expose their personal emails to everyone else on the list. In these rare cases, it's a simple, readily available solution within most email clients.
However, the limitations far outweigh the benefits for any serious email sending. When recipients reply to an email sent to 'undisclosed recipients', they might inadvertently hit 'reply all' and expose the entire BCC list if not configured correctly on the sender's side. This defeats the original purpose of privacy. Furthermore, many spam filters are increasingly wary of emails with an empty 'To:' field, as it's a tactic often employed by spammers.
For legitimate bulk communication, this method falls short. It lacks personalization, tracking capabilities, and vital authentication protocols like DMARC, SPF, and DKIM that are essential for good email deliverability. Relying on 'undisclosed recipients' suggests a lack of proper email infrastructure, which can negatively impact your sender reputation and lead to your emails being marked as spam or blocked outright.
The 'undisclosed recipients' approach
Manual process: Requires manually adding contacts to the BCC field for each email.
Limited control: No native tools for personalization, segmentation, or tracking engagement.
Deliverability risks: High chance of being flagged by spam filters due to unusual header structure and lack of authentication, leading to messages landing in the spam folder or being rejected by recipient servers.
Reply issues: Risk of accidental 'reply all' exposing all recipients.
Modern email sending platforms
Automated and scalable: Designed for managing large recipient lists and automated campaigns.
Enhanced features: Offer personalization, segmentation, A/B testing, and detailed analytics.
Optimized deliverability: Incorporate email authentication standards like SPF, DKIM, and DMARC to build sender reputation and ensure inbox placement.
Professional appearance: Emails appear professional with clear sender and recipient information.
Impact on deliverability and sender reputation
One of the most significant drawbacks of using 'undisclosed recipients' is its negative impact on email deliverability. Modern email providers, like Gmail and Outlook, use sophisticated algorithms to identify and filter spam. Emails lacking a clear recipient in the 'To:' or 'CC:' fields, relying solely on BCC, can be flagged as suspicious. This can lead to your emails being diverted to spam folders or even blocked by recipient servers, regardless of the content.
The sender's reputation is also at risk. Regular use of 'undisclosed recipients' for bulk sends can signal to email service providers that you might be engaging in questionable sending practices. A poor sender reputation can affect all your email campaigns, even those sent using proper methods. Once your domain or IP address lands on a blocklist (or blacklist), it can take considerable effort to recover.
Why 'undisclosed recipients' is a deliverability risk
Spam trigger: Emails without a direct 'To:' address are often perceived as spam by inbox providers.
Poor reputation: Consistent use can degrade your sender reputation, impacting future email campaigns.
User experience: Recipients might find it impersonal or even suspicious, leading to lower engagement.
For these reasons, it's generally best to avoid this method for any regular or critical communications. The risk to your email deliverability is too high, potentially causing important messages to be missed. There are much more effective and professional alternatives available today.
Modern alternatives for recipient privacy and bulk sending
Given the issues with 'undisclosed recipients,' it's vital to embrace modern solutions for managing recipient privacy and sending bulk emails. Email Service Providers (ESPs) and CRM platforms are specifically designed for this purpose. They handle list management, personalization, and deliverability optimization, ensuring your emails reach their intended recipients without compromising privacy or sender reputation.
These platforms allow you to send individualized emails to a large number of recipients, where each recipient sees only their own email address in the 'To:' field. This not only preserves privacy but also significantly improves deliverability rates. They also enable advanced features such as segmentation, A/B testing, and comprehensive analytics, providing valuable insights into your email campaigns.
For transactional emails or automated notifications, dedicated email APIs and services offer robust solutions. They allow you to integrate email sending directly into your applications, ensuring high deliverability, scalability, and compliance with modern email standards. Using these tools means you never have to resort to outdated methods like 'undisclosed recipients' to manage your email communications.
To further enhance your email security and deliverability, implementing and monitoring DMARC is crucial. A robust DMARC policy, along with properly configured SPF and DKIM records, authenticates your emails, telling receiving servers that your messages are legitimate and not forged. This significantly reduces the chances of your emails being marked as spam. For comprehensive DMARC monitoring and actionable insights, Suped offers an AI-powered platform with a generous free plan, helping you fix issues and strengthen your email policy efficiently.
Views from the trenches
Best practices
Always use a dedicated email service provider (ESP) for bulk email sends.
Ensure your SPF, DKIM, and DMARC records are correctly configured and monitored.
Personalize emails, even in bulk, by including the recipient's name in the 'To:' field.
Segment your audience and send relevant content to avoid spam complaints.
Regularly monitor your domain's sender reputation and blocklist status.
Common pitfalls
Sending mass emails using only the BCC field without a 'To:' or 'CC:' recipient.
Relying on 'undisclosed recipients' for professional or marketing communications.
Not configuring email authentication protocols like DMARC, SPF, and DKIM.
Ignoring bounce rates and spam complaints, which degrade sender reputation.
Using outdated systems that default to 'undisclosed recipients' for bulk sends.
Expert tips
Implement a DMARC policy with reporting to gain visibility into your email traffic.
Use email validation services to maintain a clean mailing list and avoid spam traps.
Continuously analyze your email metrics, such as open rates, click-through rates, and unsubscribes.
Educate your team on proper email sending practices and the risks of misusing BCC.
Leverage AI-powered platforms like Suped for actionable insights into email security.
Expert view
Expert from Email Geeks says 'undisclosed recipients' is merely a mail server workaround from the past to ensure syntactic correctness when no visible recipients are present. Address groups are generally obsolete and shouldn't be relied upon.
2025-11-04 - Email Geeks
Expert view
Expert from Email Geeks says seeing 'undisclosed recipients' typically means everyone was placed in BCC with no one in the To or CC fields, which is generally a bad sending practice.
2025-11-04 - Email Geeks
Conclusion
Embracing proper email practices
The concept of 'undisclosed recipients' is fundamentally tied to outdated email practices. While it served a purpose in the past for privacy, modern email security and deliverability standards have rendered it largely obsolete and even detrimental. Relying on this method for any form of bulk communication can seriously harm your sender reputation and significantly reduce your email's chances of reaching the inbox.
Moving forward, it's essential to adopt professional email sending solutions that prioritize both recipient privacy and optimal deliverability. Leveraging Email Service Providers (ESPs) for marketing and bulk communications, and ensuring robust email authentication through DMARC, SPF, and DKIM, are critical steps. Tools like Suped provide the necessary insights and capabilities to achieve this, helping you navigate the complexities of email security and ensure your messages land where they belong.
By embracing these modern practices, you not only protect recipient privacy more effectively but also build a strong, reliable sender reputation. This proactive approach is key to successful email communication in today's digital landscape, ensuring your valuable messages consistently reach your audience.
Gmail and Outlook, use sophisticated algorithms to identify and filter spam. Emails lacking a clear recipient in the 'To:' or 'CC:' fields, relying solely on BCC, can be flagged as suspicious. This can lead to your emails being diverted to spam folders or even blocked by recipient servers, regardless of the content.
