Is Email Case Sensitive? Setting The Record Straight

Can using capital letters or international characters in your email address affect your email deliverability? Does your business record high bounce rates, so you suspect the problem could be the email address format

Or do you want to add special characters to your email ID to distinguish your business from another organization with an almost similar Gmail address?

You're not alone — every email marketing service provider, business owner, or email communication expert has faced the email address syntax dilemma in one way or another. It happens to the best of us. 

So, is email case-sensitive? If you accidentally swap lowercase letters with uppercase letters in the recipient's Gmail address, will your email land in the wrong inbox? 

Read on for answers to these and other email address format-related questions. Discover the answer to the question, 'Is email case sensitive?' and learn the characters you can use in different parts of email IDs.

First, let's start by defining case sensitivity.

What Is Case Sensitivity?

Case sensitivity is the ability to discriminate between uppercase and lowercase letters. Computer programs often define characters and letters as case-sensitive or case-insensitive. 

In case sensitivity applies, the program treats small and capital letters as unique characters that are different from each other and not interchangeable, even if they are the same letters

Passwords are a great example of a real-life application of case sensitivity. Usually, most sites and apps do not allow users to swap uppercase and lowercase letters when entering their passwords. 

For instance, if your password is 'EXAMPLE,' you cannot use 'example' or 'EXamPLE.' Usually, when you accidentally tap the caps lock button, the site or app you're trying to access will prompt you to enter the correct password or lock you from your account.

Case sensitivity usually applies in logins to enhance their strength. Most apps require account holders to ensure their passwords combine small and capital letters and special characters.

Are Email Addresses Case Sensitive?

The short answer is — No; email addresses are not case-sensitive. Most email server providers' transfer protocols treat email address characters as lowercase, even when you use uppercase letters

Therefore, whether you enter, MARKTWAIN2935@DOMAIN.COM, or, email servers will interpret this as the same address.

What Is An Email Address Format?

Of course, we cannot conclusively answer the question 'Is email case sensitive' without discussing email address formats. Valid email IDs typically contain two parts:

  • The prefix: This part appears to the left of the @ symbol and usually contains the account holder's details.
  • The domain part: This section follows the @ symbol and contains the email server provider's name.

For example, if your email ID is, ‘’ is the prefix, and ‘’ is the domain part. Most email servers allow letters (a-z), periods, numbers, underscores, and special characters (~, %, !, ^, +, &, =, ", and *) in the email ID prefix. 

However, when you add a period, dash, or underscore, you must include one more number or letter before the @ symbol. Also, the domain part must have at least two characters, such as .com, .cc, or .org, whether public or own domain.

Is The Prefix Case Sensitive

The simple answer is — No; the email ID prefix has no case sensitivity. However, there are some exceptions. Consider the following email accounts containing the same address with varying uppercase and lowercase combinations.


While both follow the correct email address format and contain the same letters, some outdated email servers might wrongly misinterpret them as two unique addresses. However, this happens on very rare occasions. 

Most modern internet service providers will read them as the same mail address.

However, to be safe, we recommend avoiding crazy capitalizations. Mixing several uppercase and lowercase letters, such as in the second example above, can make reading your mail address challenging. 

The more strenuous it is for internet service providers to interpret your mail address, the more likely your emails will land in spam folders.

Is The Domain Part Case Sensitive?

Again, the short answer is — No; the mail address domain part isn't case-sensitive. The only restriction it has is it doesn't accommodate special characters

Otherwise, if you accidentally use instead of but follow the correct email address format, your email will still go to the intended recipient.

Can You Use Special Characters In Your Email Address?

Another crucial aspect of the email address syntax dilemma is whether you can use special characters. Most email marketing service providers allow the following non-Latin characters in the email IDs.

  • !
  • #
  • $
  • %
  • &
  • '
  • *
  • +
  • -
  • /
  • =
  • ?

However, you can only add these characters in the mail address's first part (prefix). Also, the special characters cannot appear as the first and last or follow one another consecutively.

Which Characters Can You Use In The Email Prefix

While the prefix is case insensitive, it can only have the following basic text language characters:

  • Uppercase Latin characters: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, and Z.
  • Lowercase Latin letters: a, b, c, d, e, f, g, h i, j, k l, m, n, o, p q, r, s, t u, v, w, x, y and z.
  • Digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9
  • Special characters: !, #, $, %, &, ', *, +, -, /, =, ?, ^, _ , `, {, |, }, ~, and ‘,’. (As long as they don't come first or last in the prefix.
  • Dot (.): It cannot be the first character in the email ID. Also, it cannot appear more than once unless you've put it in quotes.
  • Space punctuations: ", (, ), ,, :, ;, <, >, @, [, \, and ] (With some restrictions)

Which Characters Can You Use In The Domain Part

The domain section has more restrictions than the prefix. It primarily uses basic text language and international characters. The only non-Latin characters they can accommodate are 0,1, 2, 3, 4, 5, 6, 7, 8, 9, and a hyphen (-). 

However, when using the hyphen, you must precede and follow it with a number or a Latin letter. Other non-Latin characters the domain section can have are IP addresses as long as you surround it with square brackets, such as marktwain@[IPv6:2001:db8::1] or marktwain@[]

Examples of Valid vs. Invalid Email Addresses

Now that we've conclusively answered the question, 'Is email case sensitive,' let's look at a few examples for inspiration.


INVALID EMAIL IDs (Can’t start with a number or special character)

very.#? (Two special symbols can’t follow each other consecutively)$ (Special character can’t come at the end of the address) (one-letter prefix)

x@example.#com (The only special symbol usable at the domain part is a dash)


marktwain@IPv6:2001:db8::1 (You must enclose the IP address with brackets

Why Are Email Addresses Not Case Sensitive

Email servers consider all letters and characters in the address as lowercase characters. If the servers considered uppercase and lowercase letters as unique characters, any slight variation in capitalization would send emails to the wrong recipients. Case insensitivity prevents this confusion


Among the questions we’ve been answering in this guide include: Is email case sensitive? Or rather, are Gmail addresses case-sensitive?

As outlined multiple times above, and for the record, NO, they are not. Email servers interpret all letters in the address as lowercase characters. Therefore, your email will still land in the correct inboxes if you accidentally swap lowercase and uppercase letters.

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