Are email addresses case sensitive?


I know this is an old question but I just want to comment here: To any extent email addresses ARE case sensitive, most users would be "very unwise" to actively use an email address that requires capitals. They would soon stop using the address because they'd be missing a lot of their mail. (Unless they have a specific reason to make things difficult, and they expect mail only from specific senders they know.)

That's because imperfect humans as well as imperfect software exist, (Surprise!) which will assume all email is lowercase, and for this reason these humans and software will send messages using a "lower cased version" of the address regardless of how it was provided to them. If the recipient is unable to receive such messages, it won't be long before they notice they're missing a lot, and switch to a lowercase-only email address, or get their server set up to be case-insensitive.


I've read that by standard first part of e-mail is case sensitive, however I've tried to send e-mail to, and - it has arrived in each case.

How do mail servers handles usernames? Is it possible to miss with case and that message wouldn't be delivered? Is it really very important to use exactly same letter case, as was written while registering when giving your e-mail address?

I can only think of one useful reason to retrieve email with case sensitivity: Avoiding spam. Tell your friends and associates they MUST use the proper combination of upper and lower case. ( I think spammers are unlikely to follow such a rule, especially as your address gets passed around from server to server.

The drawback might be if your friends' email clients are improperly designed. Regardless of their intentions they may be unable to comply. This might be especially so with legitimate business associates who store thousands of addresses and shuffle their data around more frequently. They won't give you the same individual attention.

I won't choose to do this, but I think this would be pretty effective if you want a "friends only" email address that gets less spam. Probably not good for business contacts though.

RFC 5321 2.4. General Syntax Principles and Transaction Model

SMTP implementations MUST take care to preserve the case of mailbox local-parts. In particular, for some hosts, the user "smith" is different from the user "Smith".

Mailbox domains follow normal DNS rules and are hence not case sensitive



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