问题
What is the maximum length of a valid email address? Is it defined by any standard?
回答1:
An email address must not exceed 254 characters.
This was accepted by the IETF following submitted erratum. A full diagnosis of any given address is available online. The original version of RFC 3696 described 320 as the maximum length, but John Klensin subsequently accepted an incorrect value, since a Path is defined as
Path = "<" [ A-d-l ":" ] Mailbox ">"
So the Mailbox element (i.e., the email address) has angle brackets around it to form a Path, which a maximum length of 254 characters to restrict the Path length to 256 characters or fewer.
The maximum length specified in RFC 5321 states:
The maximum total length of a reverse-path or forward-path is 256 characters.
RFC 3696 was corrected here.
People should be aware of the errata against RFC 3696 in particular. Three of the canonical examples are in fact invalid addresses.
I've collated a couple hundred test addresses, which you can find at http://www.dominicsayers.com/isemail
回答2:
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
回答3:
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.
回答4:
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
回答5:
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.
回答6:
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)
回答7:
64 for the local part (the account/name) and 255 for the domain. I think the @ sign will be counted extra so that sums to 320.
But caution: this is only the length of the real address. An address may contain a display name. Such an address looks like first last <local@domain> and will often extend 320.
回答8:
64 characters "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.click this email site
来源：https://stackoverflow.com/questions/386294/what-is-the-maximum-length-of-a-valid-email-address