What is a plus-tagged email address and why do people use them?

Plus-tagged email addresses, like yourname+tag@example.com , are unique aliases of your primary email address. They are used to help users filter emails, organize their inbox, and identify the source of specific mail, especially spam. All emails sent to a plus-tagged address are delivered to the primary inbox.

What happens if an email sender doesn't properly handle plus-tagged addresses?

If your system doesn't normalize plus-tagged addresses, it can lead to duplicate entries in your subscriber list. This inflates your list size, skews engagement metrics, and can result in sending emails to users who believe they've unsubscribed, leading to spam complaints and potential blocklisting (or blacklisting).

How should email senders manage plus-tagged addresses for subscriptions?

You should normalize plus-tagged email addresses by stripping the '+tag' part before storing them in your database. This ensures that user+tag@domain.com and user@domain.com are recognized as the same subscriber, preventing duplicate emails and ensuring unsubscribe requests are honored.

How do plus-tagged email addresses affect the unsubscribe process?

When a user unsubscribes using a plus-tagged address, your system must normalize that address to its base form (e.g., user@domain.com ) and apply the unsubscribe to that base address. This ensures that the user stops receiving all emails from you, regardless of the specific alias they used.

Can plus-tagged addresses cause issues with the List-Unsubscribe header?

Yes, some email clients or older systems may not correctly process List-Unsubscribe headers if the email address includes a plus tag. This can cause one-click unsubscribes to fail, meaning the user won't be removed from your list even after attempting to unsubscribe through their email client.

How to use plus-tagged email addresses for subscriptions and unsubscribes? - Technical - Email deliverability - Knowledge base

Plus-tagged email addresses, also known as sub-addressing, are a powerful feature that allows email users to create unique variations of their existing email address by adding a plus sign (+) and an alphanumeric tag before the '@' symbol. For instance, if your email is yourname@example.com, you can use yourname+newsletter@example.com or yourname+shopping@example.com when signing up for services. All emails sent to these tagged addresses will still arrive in your primary inbox.

This functionality is widely supported by major email providers like Gmail,

Yahoo Mail, and Microsoft Outlook, including their enterprise versions like

Office 365. It's a useful tool for users to manage their inbox, filter incoming mail, and even identify which service might have sold or leaked their email address.

For email senders, understanding how plus-tagged addresses work is crucial for maintaining good deliverability and ensuring compliance with unsubscribe requirements. Treating yourname+tag@example.com and yourname@example.com as distinct subscribers can lead to issues, particularly when it comes to honoring unsubscribe requests.

Understanding plus addressing and its history

Plus addressing, or sub-addressing, has been around for decades, even predating modern webmail services. It's built on a standard known as RFC 5233. While the concept might seem simple, its implications for email senders are significant.

When an email is sent to a plus-tagged address, the Mail Transfer Agent (MTA) typically strips the '+tag' part before delivering it to the primary inbox. For example, an email to john.doe+shopping@example.com will land in john.doe@example.com's inbox. The user can then set up filters based on the full email address or the 'To' header to categorize or manage these emails.

This feature provides users with a powerful way to control their inbox flow. They can use unique tags for different subscriptions, making it easy to identify the source of specific emails, organize newsletters, or quickly pinpoint who might have shared their address if they start receiving unwanted mail to a specific tagged address.

What is a plus-tagged email address?

A plus-tagged email address allows you to add a unique alphanumeric string after a plus sign (+) and before the '@' sign in your email address. For example, if your primary email is jane.doe@example.com, you can use jane.doe+marketing@example.com for marketing emails. All mail sent to this unique alias still arrives in jane.doe@example.com's inbox.

Impact on subscriptions and data management

For email senders, the primary challenge with plus-tagged addresses lies in how they are stored and managed within subscriber databases. If your system treats alice+tag@example.com as a completely separate email address from alice@example.com, it can lead to duplicate entries, inaccurate engagement metrics, and, most importantly, compliance issues with unsubscribe requests.

To effectively manage subscriptions, it's a best practice to normalize these email addresses. Normalization means stripping the plus tag before storing the address in your database. This way, whether a user subscribes with user+service@domain.com or user@domain.com, they are recognized as the same individual for subscription purposes.

Failure to normalize can result in sending emails to someone who believes they have unsubscribed. This negatively impacts your sender reputation, leading to higher spam complaint rates, potential blocklisting (or blacklisting), and reduced inbox placement. Modern email service providers (ESPs) should ideally handle this normalization automatically, but it's always worth confirming how your platform manages these addresses.

Example of email normalization in JavaScriptjavascript

function normalizeEmail(email) {
  const parts = email.split('@');
  const localPart = parts[0];
  const domainPart = parts[1];

  const normalizedLocalPart = localPart.split('+')[0];

  return normalizedLocalPart + '@' + domainPart;
}

// Example usage:
const email1 = "john.doe+newsletter@example.com";
const normalized1 = normalizeEmail(email1); // john.doe@example.com

const email2 = "jane.smith@example.com";
const normalized2 = normalizeEmail(email2); // jane.smith@example.com

Handling unsubscribes and ensuring compliance

The challenge with plus-tagged addresses becomes even more pronounced when it comes to unsubscribes. Users often use these tags specifically to track email sources, and if they unsubscribe from a particular stream, they expect it to be honored for their main address as well. Not doing so can lead to frustration and direct spam complaints, which are damaging to your sender reputation.

One common issue arises with the List-Unsubscribe header, which is essential for one-click unsubscribe functionality. Some email clients or older systems might not correctly process `List-Unsubscribe` requests if the email address in the header includes a plus tag. This means a user trying to unsubscribe via the client's built-in button (which uses this header) might not be removed from your list, leading to continued unwanted emails.

This specific problem is common, and why the List-Unsubscribe header may fail with plus signs needs careful consideration. It underscores the importance of a robust unsubscribe process that handles both HTTP POST and mailto links, and correctly normalizes addresses upon receiving an unsubscribe request, regardless of the method used.

Ultimately, if a user sends an unsubscribe request from email+tag@domain.com, your system should understand that email@domain.com wishes to unsubscribe. This prevents future emails to either address from reaching them and protects your sender reputation from potential spam complaints and blocklistings.

User perspective

Users adopt plus-tags for various reasons, primarily for inbox organization and spam identification. They expect that any email sent to their primary address or a tagged alias will reach them, and conversely, that unsubscribing from one will apply to all related variations.

Expectations for privacy and control

Filtering: Easily set up rules to sort emails into folders based on the tag.
Tracking: Identify which company might be sharing or selling their email address.
Unsubscribe: Belief that unsubscribing from a tagged address should stop all emails to their main account.

Sender perspective

Senders must normalize plus-tagged addresses to prevent duplicate entries and ensure proper subscription management. Failure to do so can lead to a fragmented subscriber base and a poor user experience, especially during the unsubscribe process.

Challenges for deliverability

Compliance: Risk of violating unsubscribe laws if all address variations aren't handled.
Reputation: Increased spam complaints if users continue to receive unwanted emails.
Data Accuracy: Inflated subscriber counts and skewed engagement metrics due to duplicates.

Best practices for senders

To ensure effective subscription and unsubscribe management, senders should adopt several key practices. These actions help maintain a clean list, respect user preferences, and safeguard your sender reputation.

First, always normalize email addresses upon subscription. This means storing only the base email address (e.g., user@domain.com) in your primary subscriber list, while optionally retaining the full plus-tagged address for internal tracking or personalization. When an unsubscribe request comes in, normalize the incoming address and apply the unsubscribe to the base address.

Second, thoroughly test your unsubscribe process to ensure it functions correctly for all variations of email addresses, including plus-tagged ones. This involves verifying both in-email unsubscribe links and any preference centers or manual unsubscribe methods. Make sure that when a user clicks the one-click unsubscribe button, it successfully removes the base email from your list. Also, consider including the subscribed email address within the email body itself, which helps users confirm which address is subscribed, especially helpful for aliases. This is a common practice that can improve user experience and reduce spam complaints.

Views from the trenches

Best practices

Normalize all incoming email addresses by stripping plus tags before storing them to ensure accurate subscriber counts and prevent duplicates.

Implement a robust unsubscribe mechanism that correctly processes requests from plus-tagged addresses, applying them to the normalized base address.

Always include a functional List-Unsubscribe header in your emails to support one-click unsubscribe, crucial for email client compliance.

Display the exact email address used for subscription within the email content itself, especially useful when users utilize aliases.

Common pitfalls

Treating plus-tagged addresses as unique subscribers, leading to duplicate entries and inflated list sizes.

Failing to honor unsubscribe requests from a plus-tagged address, causing continued sending to the user's primary inbox.

Overlooking testing of unsubscribe functionality for plus-tagged addresses, resulting in broken unsubscribe paths and user frustration.

Not accounting for varying behaviors of email clients when processing List-Unsubscribe headers with plus tags, leading to failed unsubscribes.

Expert tips

Use a preference center that allows users to manage multiple subscriptions under a single normalized email, providing granular control.

Regularly audit your subscriber database for duplicate entries or inconsistencies that might arise from improper handling of aliases.

Monitor your spam complaint rates and unsubscribe rates closely, as spikes can indicate issues with how your system handles plus-tagged addresses.

Educate your customer support team on plus-addressing, so they can assist users with subscription or unsubscribe inquiries effectively.

Marketer view

Marketer from Email Geeks says now is a good time to check that subscription, sending, analytics, and unsubscribe functionality support plus-tagged email addresses correctly.

2020-07-14 - Email Geeks

Expert view

Expert from Email Geeks says that this functionality has existed for at least 25 years, so senders should already be prepared to handle these addresses.

2020-07-14 - Email Geeks

Embracing user email management strategies

Plus-tagged email addresses offer significant benefits to email users for managing their inboxes and privacy. For email senders, they represent a critical consideration for data management and deliverability. By normalizing these addresses upon subscription and ensuring that all unsubscribe mechanisms correctly handle them, you can maintain a healthy email list, improve user experience, and uphold your sender reputation.

Ignoring the nuances of plus-addressing can lead to unnecessary spam complaints and potential blocklisting (or blacklisting), impacting your ability to reach the inbox. Adapting to how users manage their email is not just about compliance, it is about building trust and fostering a positive relationship with your subscribers.