Understanding Case Sensitivity in Email Addresses

Email addresses have a specific format that must be adhered to ensure that emails reach the correct recipients. One aspect of this format that often causes confusion is the case sensitivity of email addresses. In this article, we will explore whether upper case letters in an email address will work the same as lower case letters.

Case Sensitivity in Email Addresses

When it comes to case sensitivity in email addresses, the general rule is that you must copy the email address exactly as it is written. This means that omitting or altering any character, including the case of the letters, can result in emails not reaching the intended recipient. For example:

Example 1:

Correct: JohnSmith@

Incorrect: johnsmith@

Even though JohnSmith and johnsmith might appear to be the same name, they are treated as different email addresses due to the case difference.

CASE Insensitivity and Email Service Providers

While case sensitivity is a general rule, it is not always applicable across all email service providers. Most email service providers do not distinguish between upper and lower case characters for the part of the email address after the '@' sign, commonly referred to as the host part. However, the part before the '@' sign, known as the local part, is usually case sensitive and must be written exactly as specified.

Example 2:

If you have an email address like:

Correct: JohnSmith@

And you try to send an email to:

Incorrect: johnsmith@

The email will not reach the intended recipient. However, if the issue lies with the domain part (the part after the '@' sign), it is less of a concern since most email hosts ignore case in this part.

Historical Context and Current Practices

Years ago, Unix systems enforced strict capitalization rules for email addresses. This was done to maintain consistency and to minimize errors. However, this is no longer true for modern email systems. Today, there are no longer any established rules that mandate the case of email addresses. Some legacy systems might still enforce case sensitivity, but most modern email systems default to treating email addresses as case-insensitive in the part after the '@' sign.

Example 3:

Consider the following email addresses:

Example A: JaneDoe@

Example B: janedoe@

On a modern email system, both Example A and Example B would be treated as identical. However, on a legacy system, these could be different addresses, and you might run into issues if you do not adhere to the correct case.

The Bottom Line

To avoid any confusion or issues, it is crucial to always copy email addresses exactly as they are written. This means paying close attention to the case of the letters, especially in the local part of the email address. While the host part (the part after the '@' sign) is generally case-insensitive, the local part is often case-sensitive and requires exact matching.

For the best practice, always verify the case and format of the email address with the recipient or the sender. This will help ensure that your emails are delivered successfully to the intended recipients.