Email Regular Expression

email-regex.md

Email RegEx

Go

var emailAddressRE = regexp.MustCompile(`^(?i)(?:(?:\"[^\"]+\")|[a-z0-9!#$%&'*+\-\/=?^_` + "`" + `{|}~]+(?:\.[a-z0-9!#$%&'*+\-\/=?^_` + "`" + `{|}~]+)*)@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$`)
if !emailAddressRE.MatchString("emmaly@example.com") {
  panic("oops")
}

RE2, PCRE2, PCRE, Java 8

^(?i)(?:(?:\"[^\"]+\")|[a-z0-9!#$%&'*+\-\/=?^_`{|}~]+(?:\.[a-z0-9!#$%&'*+\-\/=?^_`{|}~]+)*)@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$

ECMAScript/JavaScript

/^(?:(?:\"[^\"]+\")|[a-z0-9!#$%&'*+\-\/=?^_`{|}~]+(?:\.[a-z0-9!#$%&'*+\-\/=?^_`{|}~]+)*)@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$/i

.NET

^(?i)(?:(?:""[^""]+"")|[a-z0-9!#$%&'*+\-\/=?^_`{|}~]+(?:\.[a-z0-9!#$%&'*+\-\/=?^_`{|}~]+)*)@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$

Status

Seems to validate in basically all typical situations, but it won't validate emojis even when they're valid. See below for examples.

👍 Rejected for RHS errors

❌   emmaly@.example.com    (RHS starts with period)
❌   emmaly@example.com.    (RHS ends with period)
❌   emmaly@example..com    (RHS has two consecutive periods)
❌   emmaly@e@xample.com    (address contains two at-symbols)

👍 Rejected for LHS errors

❌   .emmaly@example.com    (LHS starts with period)
❌   emmaly.@example.com    (LHS ends with period)
❌   emmaly@@example.com    (address contains two at-symbols)

👍 Quoting the above LHS rejects will allow them to validate

✅   "emmaly."@example.com  (quoted LHS is valid)
✅   ".emmaly"@example.com  (quoted LHS is valid)
✅   "emmaly@"@example.com  (quoted LHS is valid)

👍 These are valid as expected

✅   emmaly@example.io      (valid)
✅   emma.ly@example.com    (valid)
✅   emmaly@example.com     (valid)
✅   emmaly@example.co.m    (valid, though no TLDs are 1-character long)
✅   emmaly@exa.mple.com    (valid)

🤦‍♀️ Fails to validate, but it's valid

❌   emmaly@😉.tld         (but emoji domains are technically valid)

👍 Validates because it's the punycode version of the above

✅   emmaly@xn--n28h.tld    (punycode version of emoji domain is valid)

❔ RFC 5322 says this is invalid without quotation marks; the pattern rejects it

❌   😉@example.com        (non-ASCII on LHS unless quoted is technically invalid)

(but I think we should consider treating it as valid...)

👍 It's valid if it's quoted; the pattern correctly validates it

✅   "😉"@example.com      (quoted LHS validly contains non-ASCII)

test.go

package main

import (
	"fmt"
	"regexp"
)

var emailAddressRE = regexp.MustCompile(`^(?i)(?:(?:\"[^\"]+\")|[a-z0-9!#$%&'*+\-\/=?^_` + "`" + `{|}~]+(?:\.[a-z0-9!#$%&'*+\-\/=?^_` + "`" + `{|}~]+)*)@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?)\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$`)

func main() {
	emailAddresses := []string{
		`emmaly@.example.com`,
		`emmaly@example.com.`,
		`emmaly@example..com`,
		`emmaly@e@xample.com`,
		``,
		`.emmaly@example.com`,
		`emmaly.@example.com`,
		`emmaly@@example.com`,
		``,
		`"emmaly."@example.com`,
		`".emmaly"@example.com`,
		`"emmaly@"@example.com`,
		``,
		`emmaly@example.io`,
		`emma.ly@example.com`,
		`emmaly@example.com`,
		`emmaly@example.co.m`,
		`emmaly@exa.mple.com`,
		``,
		`emmaly@😉.tld`,
		``,
		`emmaly@xn--n28h.tld`,
		``,
		`😉@example.com`,
		``,
		`"😉"@example.com`,
	}

	for _, emailAddress := range emailAddresses {
		if emailAddress == "" {
			fmt.Println()
			continue
		}

		fmt.Printf("%t\t%s\n", emailAddressRE.MatchString(emailAddress), emailAddress)
	}
}


// false   emmaly@.example.com
// false   emmaly@example.com.
// false   emmaly@example..com
// false   emmaly@e@xample.com
//
// false   .emmaly@example.com
// false   emmaly.@example.com
// false   emmaly@@example.com
//
// true    "emmaly."@example.com
// true    ".emmaly"@example.com
// true    "emmaly@"@example.com
//
// true    emmaly@example.io
// true    emma.ly@example.com
// true    emmaly@example.com
// true    emmaly@example.co.m
// true    emmaly@exa.mple.com
//
// false   emmaly@😉.tld
//
// true    emmaly@xn--n28h.tld
//
// false   😉@example.com
//
// true    "😉"@example.com