[validation] What is the maximum length of a valid email address?

What is the maximum length of a valid email address? Is it defined by any standard?

320

And the segments look like this

{64}@{255}

64 + 1 + 255 = 320

You should also read this if you are validating emails

http://haacked.com/archive/2007/08/21/i-knew-how-to-validate-an-email-address-until-i.aspx

The other answers muddy the water a bit. Simple answer: 254 total chars in our control for email 256 are for the ENTIRE email address, which includes implied "<" at the beginning, and ">" at the end. Therefore, 254 are left over for our use.

320

And the segments look like this

{64}@{255}

64 + 1 + 255 = 320

You should also read this if you are validating emails

http://haacked.com/archive/2007/08/21/i-knew-how-to-validate-an-email-address-until-i.aspx

To help the confused rookies like me, the answer to "What is the maximum length of a valid email address?" is 254 characters.

If your application uses an email, just set your field to accept 254 characters or less and you are good to go.

You can run a bunch of tests on an email to see if it is valid here. http://isemail.info/

The RFC, or Request for Comments is a type of publication from the Internet Engineering Task Force (IETF) that defines 254 characters as the limit. Located here - https://tools.ietf.org/html/rfc5321#section-4.5.3

The other answers muddy the water a bit. Simple answer: 254 total chars in our control for email 256 are for the ENTIRE email address, which includes implied "<" at the beginning, and ">" at the end. Therefore, 254 are left over for our use.

TLDR Answer

Given an email address like...

[email protected]

The length limits are as follows:

• Entire Email Address (aka: "The Path"): i.e., [email protected] -- 256 characters maximum.
• Local-Part: i.e., me -- 64 character maximum.
• Domain: i.e., example.com -- 254 characters maximum.

Source

SMTP originally defined what a path was in RFC821, published August 1982, which is an official Internet Standard (most RFC's are only proposals). To quote it...

...a reverse-path, specifies who the mail is from.

...a forward-path, which specifies who the mail is to.

RFC2821, published in April 2001, is the Obsoleted Standard that defined our present maximum values for local-parts, domains, and paths. A new Draft Standard, RFC5321, published in October 2008, keeps the same limits. In between these two dates, RFC3696 was published, on February 2004. It mistakenly cites the maximum email address limit as 320-characters, but this document is "Informational" only, and states: "This memo provides information for the Internet community. It does not specify an Internet standard of any kind." So, we can disregard it.

To quote RFC2821, the modern, accepted standard as confirmed in RFC5321...

4.5.3.1.1. Local-part

The maximum total length of a user name or other local-part is 64 characters.

4.5.3.1.2. Domain

The maximum total length of a domain name or number is 255 characters.

4.5.3.1.3. Path

The maximum total length of a reverse-path or forward-path is 256 characters (including the punctuation and element separators).

You'll notice that I indicate a domain maximum of 254 and the RFC indicates a domain maximum of 255. It's a matter of simple arithmetic. A 255-character domain, plus the "@" sign, is a 256-character path, which is the max path length. An empty or blank name is invalid, though, so the domain actually has a maximum of 254.

According to the below article:

http://tools.ietf.org/html/rfc3696 (Page 6, Section 3)

It's mentioned that:

"There is a length limit on email addresses. That limit is a maximum of 64 characters (octets) in the "local part" (before the "@") and a maximum of 255 characters (octets) in the domain part (after the "@") for a total length of 320 characters. Systems that handle email should be prepared to process addresses which are that long, even though they are rarely encountered."

So, the maximum total length for an email address is 320 characters ("local part": 64 + "@": 1 + "domain part": 255 which sums to 320)

320

And the segments look like this

{64}@{255}

64 + 1 + 255 = 320

You should also read this if you are validating emails

http://haacked.com/archive/2007/08/21/i-knew-how-to-validate-an-email-address-until-i.aspx

According to the below article:

http://tools.ietf.org/html/rfc3696 (Page 6, Section 3)

It's mentioned that:

"There is a length limit on email addresses. That limit is a maximum of 64 characters (octets) in the "local part" (before the "@") and a maximum of 255 characters (octets) in the domain part (after the "@") for a total length of 320 characters. Systems that handle email should be prepared to process addresses which are that long, even though they are rarely encountered."

So, the maximum total length for an email address is 320 characters ("local part": 64 + "@": 1 + "domain part": 255 which sums to 320)

user

The maximum total length of a user name is 64 characters.

domain

Maximum of 255 characters in the domain part (the one after the “@”)

However, there is a restriction in RFC 2821 reading:

The maximum total length of a reverse-path or forward-path is 256 characters, including the punctuation and element separators”. Since addresses that don’t fit in those fields are not normally useful, the upper limit on address lengths should normally be considered to be 256, but a path is defined as: Path = “<” [ A-d-l “:” ] Mailbox “>” The forward-path will contain at least a pair of angle brackets in addition to the Mailbox, which limits the email address to 254 characters.

To help the confused rookies like me, the answer to "What is the maximum length of a valid email address?" is 254 characters.

If your application uses an email, just set your field to accept 254 characters or less and you are good to go.

You can run a bunch of tests on an email to see if it is valid here. http://isemail.info/

The RFC, or Request for Comments is a type of publication from the Internet Engineering Task Force (IETF) that defines 254 characters as the limit. Located here - https://tools.ietf.org/html/rfc5321#section-4.5.3

TLDR Answer

Given an email address like...

[email protected]

The length limits are as follows:

• Entire Email Address (aka: "The Path"): i.e., [email protected] -- 256 characters maximum.
• Local-Part: i.e., me -- 64 character maximum.
• Domain: i.e., example.com -- 254 characters maximum.

Source

SMTP originally defined what a path was in RFC821, published August 1982, which is an official Internet Standard (most RFC's are only proposals). To quote it...

...a reverse-path, specifies who the mail is from.

...a forward-path, which specifies who the mail is to.

RFC2821, published in April 2001, is the Obsoleted Standard that defined our present maximum values for local-parts, domains, and paths. A new Draft Standard, RFC5321, published in October 2008, keeps the same limits. In between these two dates, RFC3696 was published, on February 2004. It mistakenly cites the maximum email address limit as 320-characters, but this document is "Informational" only, and states: "This memo provides information for the Internet community. It does not specify an Internet standard of any kind." So, we can disregard it.

To quote RFC2821, the modern, accepted standard as confirmed in RFC5321...

4.5.3.1.1. Local-part

The maximum total length of a user name or other local-part is 64 characters.

4.5.3.1.2. Domain

The maximum total length of a domain name or number is 255 characters.

4.5.3.1.3. Path

The maximum total length of a reverse-path or forward-path is 256 characters (including the punctuation and element separators).

You'll notice that I indicate a domain maximum of 254 and the RFC indicates a domain maximum of 255. It's a matter of simple arithmetic. A 255-character domain, plus the "@" sign, is a 256-character path, which is the max path length. An empty or blank name is invalid, though, so the domain actually has a maximum of 254.