The use of capital letters within the local part (before the @ symbol) of an email address is a topic of technical specification and practical interpretation. While the official standards, such as those defined in RFC 5321 and RFC 5322, technically allow for these characters, the interpretation and support vary among email providers and systems. For example, an address might appear as “John.Smith@example.com,” but whether the email system treats “John.Smith,” “john.smith,” and “John.SmiTh” as identical is implementation-dependent.
The primary importance lies in ensuring consistent and reliable email delivery. A lack of uniformity in how email systems handle capitalization can lead to undelivered messages, miscommunication, and potential security vulnerabilities. Historically, the early days of email saw a greater emphasis on case sensitivity. However, modern email systems generally treat the local part as case-insensitive for practical reasons, simplifying address management and reducing user errors. This evolution balances strict adherence to the standard with the need for usability.
