Are email addresses case sensitive?
Short answer: almost never in real life. JohnSmith@Gmail.com and johnsmith@gmail.com reach the same inbox. The technical rules are a bit more interesting, and there is one practical reason to type addresses in lowercase anyway.
The domain (after the @) is never case sensitive: GMAIL.COM and gmail.com are the same. The local part (before the @) is allowed to be case sensitive by the email standard, RFC 5321, but the same standard says using that "impedes interoperability and is discouraged." In practice, mail servers treat John.Smith and john.smith as the same mailbox. Type and store addresses in lowercase to be safe.
The two parts of an email address
The local part is the mailbox name. The domain says which mail server handles it. The rules about capital letters are different for each half. For more on the parts, see what is an email address?
The domain is never case sensitive
Domain names work through DNS, the internet's address book. The DNS standard (RFC 1035) says comparisons between domain names are done "in a case-insensitive manner." So @Gmail.com, @GMAIL.COM and @gmail.com all point to the same place. You can't break an address by capitalizing the domain.
The local part: what the rules say
RFC 5321, the standard for sending email (SMTP), says in section 2.4:
- "The local-part of a mailbox MUST BE treated as case sensitive."
- "However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged."
Put simply: a server passing mail along must keep your capital letters exactly as you typed them, because the receiving server has the final say on what they mean. A receiving server could, in theory, treat John and john as two different people. The standard warns against doing that, and mainstream providers don't.
Why would the standard allow case sensitivity at all?
The standard doesn't tell a mail server how to name its mailboxes. It leaves that decision to the server that owns the mailbox, so a system that treats Report and report as different names isn't breaking the rules.
What it does insist on is that servers in the middle (the ones that pass your message along) never change your capital letters. Only the final server decides what they mean. That's also why the same standard warns that actually relying on case differences "impedes interoperability": people type addresses from business cards, phone calls and memory, and they won't get the capitals right.
Today, mainstream providers pick the friendly option. You'll almost never meet a server that treats Sam and sam as two people.
What happens in practice
- Sending: if you type
Maria.Lopez@Outlook.com, it arrives in the same inbox asmaria.lopez@outlook.com. - Gmail: Google's username rules allow letters (a-z), numbers and periods. Google also says that dots don't matter in personal @gmail.com addresses: mail to a dotted version still reaches you.
- Passwords are different: your password is case sensitive. Google's account recovery tips, for example, remind you to pay attention to uppercase and lowercase letters when typing a password.
- Company mail servers: a very old or unusual server could treat case differently. It's rare, but it's why the standard is worded so carefully.
Quick test: if you're unsure about an address, email it once in lowercase. If it bounces, the problem is almost certainly a typo, not the capitals.
Examples: same inbox or not?
| You type | Real address | Same inbox in practice? |
|---|---|---|
Maria.Lopez@Gmail.com | maria.lopez@gmail.com | Yes (capitals don't matter) |
MARIA.LOPEZ@GMAIL.COM | maria.lopez@gmail.com | Yes |
marialopez@gmail.com | maria.lopez@gmail.com | Yes for personal Gmail (Google says dots don't matter) |
marialopez@company.com | maria.lopez@company.com | Not necessarily: Google says dots do change addresses on work and school accounts |
maria.lopes@gmail.com | maria.lopez@gmail.com | No, that's a different address (typo) |
The lesson: capital letters are almost never the problem. Missing or extra letters, dots on non-Gmail addresses, and wrong domains are.
When capitalization can cause problems
The real trouble isn't delivery. It's software that compares addresses as text:
- Duplicate contacts: a spreadsheet or CRM may see
Sam@Shop.comandsam@shop.comas two people, so they get your newsletter twice. - Website logins: a site might store your address as typed and fail to find your account if you sign in with different capitals.
- Unsubscribes: if the unsubscribe list and the mailing list don't match case, someone may keep getting mail after opting out.
The fix is simple: convert addresses to lowercase before you compare, de-duplicate or import them. Our guide to cleaning an email list covers the rest.
Practical advice
- When you give out your address, write it in lowercase so nobody wonders.
- Capitals for readability are fine on business cards and signatures, such as
Info@BaysideDental.com. It'll still work. - When you collect addresses on a form or in a spreadsheet, store them in lowercase.
- When an email bounces, look for typos, extra spaces and wrong domains (gmial.com) before blaming capital letters. See valid email address characters for what's allowed.
Questions people ask
- Does capitalization matter in an email address?
- In practice, no. Mail reaches the same inbox whether you use capitals or not. The domain is never case sensitive, and providers treat the part before the @ as case-insensitive.
- Are Gmail addresses case sensitive?
- Not in practice. Gmail usernames are made of letters, numbers and periods, and capital letters in the address don't send mail to a different person.
- Is the part before the @ case sensitive?
- The email standard (RFC 5321) allows it, but says relying on it is discouraged. Mainstream providers don't.
- Is my email password case sensitive?
- Yes. Passwords are case sensitive even though the address isn't.
- Should I store email addresses in lowercase?
- Yes. It prevents duplicate contacts and mismatches in logins and unsubscribe lists.