The practice of using uppercase characters within the username portion of an electronic mail address is generally unsupported by modern email systems. While domain names are case-insensitive, the part preceding the “@” symbol, the local-part, technically allows for case sensitivity according to older specifications. For example, “ExampleUser@example.com” and “exampleuser@example.com” could, in theory, refer to different mailboxes. However, in practice, most providers treat them as identical, converting them to lowercase for consistency.
The importance of this lies in ensuring reliable email delivery and avoiding potential confusion. Reliance on case sensitivity introduces the risk of undelivered messages or misdirected communication if the recipient’s email system interprets uppercase letters differently. The historical context reveals that early email protocols permitted case sensitivity, but the subsequent widespread adoption of Simple Mail Transfer Protocol (SMTP) and related standards has led to a de facto standard of case-insensitivity for the local-part, prioritizing interoperability and reducing errors.