Why does list-unsubscribe header not work with a plus sign in Gmail?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Apr 2025
Updated 16 Aug 2025
7 min read
The List-Unsubscribe header is a critical component of modern email deliverability, offering recipients a clear and easy way to opt out of unwanted communications. Email clients like Gmail often display this unsubscribe button prominently at the top of the message interface, making it a user-friendly alternative to finding a tiny link in the email footer. However, a specific technical challenge arises when email addresses include a plus sign (e.g., user+tag@example.com). This seemingly minor detail can prevent the List-Unsubscribe header from functioning as intended, leading to frustrated subscribers and potential deliverability issues.
The problem stems from how some email service providers (ESPs) or internal mailing list systems parse these plus-tagged addresses. While Gmail itself understands that user+tag@example.com and user@example.com often refer to the same inbox, many mailing list management systems do not automatically equate them. This disconnect means an unsubscribe request originating from the plus-tagged address might not be recognized or processed against the main email address on file.
This article will explore the mechanics behind plus-tagged addresses, the functioning of the List-Unsubscribe header, and crucially, why these two elements sometimes clash in the Gmail environment, hindering your email deliverability and reputation.
The role of plus-tagged email addresses
Plus-tagged email addresses are a simple yet powerful feature supported by many email providers, including Gmail. They allow users to append a string (or 'tag') to their email address using a plus sign before the '@' symbol, like yourname+tag@gmail.com. All emails sent to these tagged addresses still arrive in the primary inbox (yourname@gmail.com), but the tag remains visible in the recipient's view. This feature is widely used for filtering, tracking, and managing subscriptions.
For instance, someone might subscribe to a newsletter using myemail+newsletter@gmail.com. This allows them to easily identify the source of emails and set up inbox rules to automatically categorize or filter them. It also provides a way to trace if an email address has been shared or sold, as they can track which tagged address received spam.
While beneficial for users, the presence of the plus sign can introduce complexities for email sending systems. Many systems are designed to process email addresses as exact strings, and might not automatically normalize user+tag@domain.com to user@domain.com for internal operations, especially for unsubscribe requests.
How list-unsubscribe headers function
The List-Unsubscribe header (sometimes called a blocklist or blacklist header) is a standard email header designed to provide an easy, one-click unsubscribe mechanism for recipients. It is defined in RFC 8058 and widely adopted by major mailbox providers, including Gmail and Yahoo. These providers increasingly require its proper implementation, particularly for bulk senders.
There are two primary forms of the List-Unsubscribe header:
Mailto link: This uses a mailto: address, which generates an email from the recipient's email client to the specified address. The subject line often includes 'unsubscribe' to automate the process.
HTTP URL: This directs the user to a web page where they can confirm their unsubscribe request, often with a single click. This is increasingly preferred due to its simplicity and automation.
For bulk senders, compliance with these requirements is paramount. Mailbox providers, including Google and Yahoo, have stipulated that by June 2024, bulk senders must support one-click list-unsubscribe functionality via the List-Unsubscribe header. Failure to comply can result in emails being sent directly to the spam folder or even outright rejection.
The core issue when the List-Unsubscribe header fails with plus-tagged addresses lies in how the receiving ESP or mailing list system processes the unsubscribe request. When Gmail or another client triggers the unsubscribe, it sends either an email to the mailto: address or makes an HTTP request to the URL specified in the header. Crucially, this request originates from the exact email address that received the original message, including the plus tag.
Many legacy or poorly configured systems are not designed to automatically normalize plus-tagged addresses. This means that if a user subscribed with user@example.com, but their email client triggers an unsubscribe from user+newsletter@example.com, the system might not find a match in its active subscriber list. As a result, the unsubscribe request is ignored, and the user continues to receive emails.
The issue is less about Gmail's handling of the plus sign and more about the receiving system's inability to recognize that the primary email address and its plus-tagged variations point to the same subscriber. This becomes a significant problem for user experience and can lead to increased spam complaints, as users resort to marking emails as spam when direct unsubscribe methods fail.
How it should work
A robust ESP or mailing list system should automatically parse the email address submitted for unsubscribe. This involves removing any plus tags and dots (for Gmail addresses) before attempting to match it against its subscriber database. This ensures that user+tag@example.com correctly unsubscribes user@example.com.
Why it might not work
Some ESPs or custom mailing list software may perform a literal match for the email address. If the unsubscribe request comes from user+tag@example.com, but the subscriber is recorded as user@example.com, the system fails to find a match and does not process the unsubscribe. This can also occur with the period (dot) handling in Gmail addresses (e.g., user.name@gmail.com vs. username@gmail.com).
Impact on deliverability and sender reputation
When List-Unsubscribe fails, the immediate consequence is a negative user experience. Subscribers who feel trapped on a list because they can't easily opt out are more likely to mark your emails as spam. This directly harms your sender reputation, a crucial factor in email deliverability.
Mailbox providers closely monitor spam complaint rates. High complaint rates signal to providers like Gmail that your emails might be unwanted or that your sending practices are poor. This can lead to your emails being filtered into the spam folder for all recipients, even those who want to receive them. Over time, consistent failures in unsubscribe mechanisms can result in your domain or IP address being added to an email blocklist (or blacklist), severely impacting your deliverability.
Regulatory bodies also take unsubscribe compliance seriously. For example, the CRTC recently fined Gap for failing to properly manage unsubscribes. Ensuring that your List-Unsubscribe header works for all valid email formats, including plus-tagged addresses, is not just a best practice, but a critical compliance requirement to maintain a healthy email program.
Addressing the problem
If you suspect this issue is affecting your List-Unsubscribe functionality, here's what you can do:
Contact your ESP: Inquire about their handling of plus-tagged email addresses for unsubscribe requests and if their system normalizes them.
Test thoroughly: Send test emails to a plus-tagged address and attempt to unsubscribe using the List-Unsubscribe header. Monitor your ESP's logs to confirm the request is received and processed correctly.
Ensure proper implementation: Verify that your List-Unsubscribe header is correctly formatted and includes both the mailto: and HTTP URL options as recommended by Gmail and Yahoo.
Ensuring proper unsubscribe functionality
Ensuring your List-Unsubscribe header works seamlessly, even for plus-tagged email addresses, is fundamental for maintaining a healthy email program and positive sender reputation. By understanding how these addresses are handled (or mishandled) by your ESP, you can proactively address potential issues and ensure a smooth unsubscribe experience for all your subscribers.
Views from the trenches
Best practices
Ensure your ESP normalizes plus-tagged email addresses for unsubscribe requests.
Implement both mailto: and HTTP URL options in your List-Unsubscribe header.
Regularly test your unsubscribe process with various email addresses, including plus-tagged ones.
Common pitfalls
ESPs performing exact matches on email addresses, ignoring plus tags and dots.
Not recognizing the RFC 8058 standard for one-click unsubscribes.
Failing to process unsubscribe requests from specific email clients like Gmail.
Expert tips
Always include a clearly visible unsubscribe link within the email body as a fallback.
Provide an unsubscribe confirmation message or page for clarity.
Review your bounce and complaint data for anomalies after changes to your unsubscribe process.
Marketer view
A marketer from Email Geeks says they found their list-unsubscribe header wasn't working in Gmail when a plus sign was added to the email address, and they were trying to determine if the unsubscribe was not being sent or if their ESP was mishandling it.
2022-01-20 - Email Geeks
Expert view
An expert from Email Geeks says they have seen this issue before, recalling it was a problem with how the ESP handles plus-tagged addresses, and that understanding how the mailto link is created is key.
2022-01-20 - Email Geeks
Key takeaways for robust unsubscribes
The seemingly small detail of a plus sign in an email address can create a significant obstacle for List-Unsubscribe functionality in Gmail, primarily due to how various ESPs process these unique email formats. By ensuring your systems correctly normalize plus-tagged addresses for unsubscribe requests, you not only improve user experience but also safeguard your sender reputation and comply with evolving email deliverability standards. Prioritizing robust unsubscribe mechanisms is a cornerstone of responsible and effective email sending.
Gmail. They allow users to append a string (or 'tag') to their email address using a plus sign before the '@' symbol, like yourname+tag@gmail.com. All emails sent to these tagged addresses still arrive in the primary inbox (yourname@gmail.com), but the tag remains visible in the recipient's view. This feature is widely used for filtering, tracking, and managing subscriptions.
Yahoo. These providers increasingly require its proper implementation, particularly for bulk senders.
Google and 
Yahoo, have stipulated that by June 2024, bulk senders must support one-click list-unsubscribe functionality via the List-Unsubscribe header. Failure to comply can result in emails being sent directly to the spam folder or even outright rejection.
Gmail and Yahoo.
