Are Emails Case Sensitive?

There is a lot of confusion over whether email addresses are case sensitive or not. Some say they are, while others claim that they aren’t. So, who is right? In this article we’ll take a look into whether email addresses are case sensitive or case insensitive.

Are Emails Case Sensitive?

What Makes an Email Address?

An email address is made up of three parts – the local part (also known as username), the @ sign, and the domain part. Each part has its own role and is subject to its own set of rules. Here’s a quick overview.

According to the standard, the local part of the email address can be up to 64 characters long and can be made up of a limited set of characters. These include upper and lower case Latin alphabet letters, numbers from 0 to 9, dot, and special characters. The special characters include `!@#$%^&*()_-+=[]{}~. It is connected to the domain part with the @ sign.

The domain part can be up to 255 characters long. It can contain letters of the Latin alphabet (both lower and upper case), numbers from 0 to 9, and hyphen. The hyphen can’t start or end the domain part.

International symbols can also be used, though more on that later.

Is It Case Sensitive?

The correct answer to this question is both yes and no. According to RFC 5321, the local part of the email address is case sensitive. This means that, in theory, [email protected] is not the same as [email protected]. However, email providers have the liberty to treat the local parts as both case sensitive and case insensitive.

For example, [email protected], [email protected], and [email protected] are theoretically different email addresses. It is easy to see how this could create problems and diminish user experience if a mail server opted to treat the local parts as case sensitive. Therefore, many providers treat the local part of the email address as case insensitive.

As for the domain part, RFC 1035 stipulates that it is always case insensitive. This means that you can write it in lower case, upper case, or any combination of the two and your email will end up at the same address. In practical use, [email protected], [email protected], and [email protected] are the same email address.

In Practice

While email addresses are only partially case-sensitive, it is generally safe to think of them as case insensitive. All major providers, such as Gmail, Yahoo Mail, Hotmail, and others, treat the local parts of email addresses as case insensitive. That being said, you should check the rules of the email provider with which you want to create an email.

Tying into the previous point, the above mentioned RFC 5321 recommends for new email addresses to be created with lower case letters only to avoid potential confusion and delivery problems.

On the other hand, if your friend or colleague has an email address with a combination of upper case and lower case characters, it is advisable to write it as it is when you’re sending them an email. Failure to do so might cause the email to not be delivered. However, this is not an issue with major email providers like Gmail, Yahoo Mail, Hotmail, and others.

Additionally, Gmail is also insensitive to dots found in the local part of the email when it comes to user account identification. This means that if the [email protected] account exists, you won’t be able to register [email protected] or [email protected].


Originally, email addresses could only be registered using the letters of the Latin alphabet, numbers, and a limited set of special ASCII characters. However, the IETF (Internet Engineering Task Force) has subsequently developed rules and standards for inclusion of international characters.

RFC6530 was the first to include and regulate the use of international characters. RFC6531 expanded on the rules and standards. Subsequently, the rules and standards were updated through RFC6532 and RFC6533.

You can now register an email address using a wide range of alphabets, characters, and scripts. Some of the most widely used include Latin characters with diacritics, Greek alphabet, Traditional Chinese characters, Japanese characters (hiragana, katakana, and kanji), Cyrillic alphabet, several Indian scripts, as well as a range of others.

The inclusion of and compatibility with international email addresses varies from provider to provider. Even some of the biggest providers are not fully compatible with international addresses. For example, Google allows you to send an email to an international address but it doesn’t allow you to create one. Outlook 2016 has a similar functionality.


Unlike the domain name part, the local part of an email address is case sensitive. That being said, many email providers choose to ignore the case sensitivity of the local part for practical reasons and encourage people to create emails with lower case characters only.

2 thoughts on “Are Emails Case Sensitive?”

Jim Santoro says:
I used to think expressing email addresses in upper and lower case was wonderful. They were easier to decipher, easier to remember and helped to avoid some awkward mashups of first initial+last name.
But, most of the world doesn’t understand they’re functional either way. And if your customers, friends, etc., think they need to preserve the uc/lc format when they enter the email address (especially on a device), you’ve caused more trouble and delay.
Andrea says:
I always wanted to know this. I usually just keep it all lower case and even ignore the person if they tell me “capital A” and continue. Now I know that I should pay better attention.

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