Gmail IDs are case-sensitive

Is it okay to use capital letters in an email address?

[email protected] / [email protected]

Technically, these are different email addresses, but they are probably in Order.

The domain part of the email address (example.com) is different not between Large and lower case. So "ExaMple.com" is the same as "example.com". Because the recipient (local part) may be case-sensitive, "hello" is different from "hello". However, real mail servers tend not to enforce this (I've never found one to do this) - as it is simply confusing and prone to user error.

If you save e-mail addresses, you should keep them in the original box (at least with the recipient) for security reasons. However, always compare them case-insensitive to avoid duplicates.

From RFC 2821 - Simple Mail Transfer Protocol:

The local part of a mailbox MUST be treated as case sensitive. Therefore, SMTP implementations MUST ensure that the case of local parts of the mailbox is preserved. Mailbox domains are not case-sensitive. For some hosts in particular, the "smith" user is different from the "Smith" user. However, capitalizing on local parts of the mailbox affects interoperability and is not recommended.