Understanding Valid Email Address Formats: A Short Guide

Email has become an integral part of our daily lives, serving as a primary means of communication in both personal and professional spheres. To ensure the efficient exchange of information, it’s crucial to understand what constitutes a valid email address format. In this comprehensive guide, we’ll delve into the essential components of a valid email address, rules to follow, and some common misconceptions.

The Anatomy of an Email Address

An email address consists of two main parts: the local part and the domain part. These two components are separated by the “@” symbol. Let’s break down the anatomy of an email address:

1. Local Part

The local part represents the user’s unique identifier within a specific email domain. It can include:

  • Alphanumeric Characters: Letters (A-Z, a-z) and numbers (0-9) are typically allowed in the local part.
  • Special Characters: Certain special characters, such as periods (.), underscores (_), and hyphens (-), are often permitted within the local part. For example, “john.doe@example.com” and “jane_doe@example.com” are both valid.
  • Case Sensitivity: Email addresses are generally not case-sensitive, meaning “JohnDoe@example.com” is equivalent to “johndoe@example.com.”

2. Domain Part

The domain part specifies the mail server that receives and handles emails for a particular domain. It consists of:

  • Domain Name: This is typically a combination of alphanumeric characters and hyphens, separated by periods. For instance, in “example.com,” “example” is the second-level domain, and “com” is the top-level domain.
  • Top-Level Domain (TLD): The TLD is the last part of the domain name (e.g., .com, .org, .net). TLDs can consist of letters only or a combination of letters and numbers.
Valid Email Address Formats - email icon
Photo by Brett Jordan on Unsplash

If you want to know more about the valid domain part and how many characters can contain a fully qualified domain name, read our other article.

Rules for Valid Email Addresses

Now that we covered the basic structure of an email address, let’s explore the rules that govern valid email address formats:

  1. Minimum Length: An email address should consist of at least one character in the local part, followed by the “@” symbol, and then the domain part. However, it cannot be empty.
  2. Maximum Length: The maximum length for an email address is typically 320 characters. This includes both the local and domain parts.
  3. No Spaces: Spaces are not allowed in email addresses.
  4. Special Characters: Special characters like periods, underscores, and hyphens are permitted in the local part, but they cannot be the first or last character in the local part, and they cannot appear consecutively (e.g., “..” or “__”).
  5. Domain Rules: The domain part must follow specific rules, including a valid domain name and a valid TLD. The TLD should consist of 2 to 63 characters.
  6. Case Insensitivity: Email addresses are generally not case-sensitive. “user@example.com” is the same as “User@Example.com.”
  7. Valid Characters: Ensure that the characters used are within the allowed range of ASCII characters.

Common Misconceptions

  1. Quotes and Brackets: While some email systems allow quotes and brackets in the local part (e.g., “john.doe”@example.com or john[dot]doe@example.com), they are not universally accepted.
  2. Unicode Characters: Unicode characters (non-ASCII characters) can be used in email addresses, but their compatibility depends on the email service provider and the recipient’s email client.
  3. IP Addresses: In some cases, email addresses can be in the format user@[IPv4] or user@[IPv6] to specify an IP address as the recipient. However, this is relatively rare.
  4. Comments: Some email systems allow comments enclosed in parentheses within the local part (e.g., john.doe(comment)@example.com). However, this is not a standard practice.

Recognizing a valid email address format with an API

It’s all fine and dandy when you need to recognize a few email addresses. But what about when you need to validate thousands of email addresses? Then we need the help of AI, software, and APIs (Email Validation API in particular). For the past 10 years we’ve been building APIs, so at one point we’ve created Email Score API. After all, email reputation and domain name reputation is critical!

With an Email Score API you can detect if an email address is created with a disposable email service, a free service like Gmail or the email resides on a popular domain name.

Email scoring
Email scoring

Plus (+), a bonus part

A neat little trick that you can use when signing up for any service is to create an alias. For example, when you sign up for WhoAPI service, you can use the following whoapi+john.doe@example.com. Instead of john.doe@example.com you would obviously put your email address.

And instead of “whoapi” you can put any service that you sign up for. That you it will be easier to filter emails coming from certain services, and you can recognize if the email is coming from somewhere else.

For more tips on emails, you can read my other articles on Inbox Zero and How To Pick The Best Email Address.


Understanding what constitutes a valid email address format is essential for effective communication in the digital age. By adhering to the established rules and guidelines, you can ensure that your email addresses are correctly formatted and ready for successful delivery. While there are variations and exceptions, following the standard conventions will ensure your emails reach their intended recipients with minimal issues.


Goran Duskic has been the Founder and CEO of WhoAPI Inc. since 2011, a company that specializes in developing APIs, including the well-known Whois API. He started his career in internet entrepreneurship in 2006 and has co-founded several online businesses, including a web hosting company that he later sold. Goran's work primarily involves creating practical API solutions to meet technological needs.