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Introduction

In the context of Open Email Standards, most meta tags are not allowed due to the security risks they pose. Certain meta tags can introduce vulnerabilities like unauthorized redirection, cookie setting, or security policy manipulation.

Recommended Meta Tags in an Email Context

<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta name="title" content="Welcome to Our Newsletter">
	<meta name="referrer" content="no-referrer-when-downgrade">
	<title>Welcome to Our Newsletter</title>
</head>

Meta Tags to Avoid

  • <meta http-equiv="refresh">: Automatically redirects or refreshes the page after a set time. This can be exploited for phishing attacks or malicious redirects.
  • <meta http-equiv="content-security-policy">: Used to define a content security policy (CSP), which can override the security measures of the email client and potentially introduce vulnerabilities.
  • <meta http-equiv="set-cookie">: Sets cookies via HTTP headers. This can introduce privacy issues by tracking user behavior in ways that bypass standard consent mechanisms.

Optional Meta Tags

  • <meta charset="UTF-8">: Ensures correct display of special characters. While not always necessary, it may still be required by some clients, such as Thunderbird, for proper rendering.
  • <meta name="viewport">: Optimizes email display on different devices. While some email clients that render content within an <iframe> may not require this tag, it remains beneficial for ensuring optimal display in others.
  • <meta name="title">: Provides an optional method to define the email's subject, particularly for web-based email clients or specialized contexts. Similarly, the <title> tag–commonly used in web pages–is optional in emails and offers limited utility beyond what the Subject header provides.

Meta Tags Under Consideration

  • <meta name="referrer">: Controls how much referrer information is passed when the user clicks on a link. The option no-referrer-when-downgrade can enhance user privacy by limiting the referrer data sent in certain situations.
  • Why Consider: It can enhance user privacy by restricting the information shared with third-party websites when users click links in the email, but it may not be critical in every case.

Irrelevant Meta Tags for Email

  • <meta name="theme-color">: This controls the browser UI, which is irrelevant to email clients.
  • <meta http-equiv="expires">, <meta http-equiv="pragma">: These tags control caching behavior, which does not typically apply in email.
  • Tags related to SEO and social media, like those for search engine optimization or open graph metadata, are irrelevant for email clients. Similarly, browser-specific tags, such as those that control UI elements or define caching behavior, serve no purpose in an email environment and should be excluded.