What is the right domain length?

[michaeljota]

According to this guy the domain length should be 254 chars at most, but the isEmail function it's checking for a 256 chars length, that is was once considered ok, but it seems like it was an errata

Which one is correct?

[chriso]

It sounds like it should be 254.

[korvent]

You misunderstood. It is said:

What is the length of an email address? The correct answer seems to be in the errata with ID 1690 from RFC 3696: "[...] the upper limit on address lengths should normally be considered to be 254."

This does not concern the length of the domain part but the entire email address.

Furthermore there is an error in this errata: RFC 2821 says (https://tools.ietf.org/html/rfc2821#page-17):

RCPT TO:<forward-path> [ SP <rcpt-parameters> ] <CRLF> The first or only argument to this command includes a forward-path (normally a mailbox and domain, always surrounded by "<" and ">" brackets) identifying one recipient.

and (https://tools.ietf.org/html/rfc2821#page-55):

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

so the total length of forward-path (the email address) is well 256 and not 254.

Concerning the domain length: RFC 3696 says (https://tools.ietf.org/html/rfc3696#page-5):

A complete, fully-qualified, domain name must not exceed 255 octets.

RFC 2821 says (https://tools.ietf.org/html/rfc2821#page-55):

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

In summary:

• "local part" (before the "@") has a maximum of 64 characters (octets); => https://tools.ietf.org/html/rfc3696#page-7
• "domain part" (after the "@") has a maximum of 255 characters (octets); => https://tools.ietf.org/html/rfc3696#page-7
• total length ("local part" + "@" + "domain part") is restricted to 256 characters (due to a restriction in RFC 2821 on the length of an address in MAIL and RCPT commands). => https://tools.ietf.org/html/rfc2821#page-55

References https://tools.ietf.org/html/rfc3696#page-5 https://tools.ietf.org/html/rfc2821#page-17 https://tools.ietf.org/html/rfc2821#page-55

[ezkemboi]

I will try to do more investigation on how to solve this bug.

[sakhmedbayev]

It seems it supports only 64 characters long domain parts, so it supports the same length for both local and domain parts???

[WikiRik]

The 'domain part' is allowed to be longer than 64 characters, see the following part of the source code; https://github.com/validatorjs/validator.js/blob/531dc7f1f75613bec75c6d888b46480455e78dc7/src/lib/isEmail.js#L135-L140