Is there a difference in the email domain spelling format?

Question

gmail

The bottom line is that there is an email address to which the letter was sent, but the format of writing this address is a bit unusual: the domain name contains upper and lower case (Note: [email protected]). When sending an email, Gmail automatically changed the domain to @mycompany.com. Question: is there a difference in the format of writing such domains and did the letter reach the right place? Thank you.

Answer 1

By RFC 2821, the box (that is, whatever comes before @) is case -sensitive . That is, [email protected] and [email protected] should be treated as different boxes. But, usually, mail services ignore this protocol rule in order to avoid discrepancies, and such addresses are equivalent.
According to RFC 1035, the domain is case -insensitive .