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("[email protected]") {
  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

❌   [email protected]    (RHS starts with period)
❌   [email protected].    (RHS ends with period)
❌   [email protected]    (RHS has two consecutive periods)
❌   emmaly@[email protected]    (address contains two at-symbols)

👍 Rejected for LHS errors

❌   [email protected]    (LHS starts with period)
❌   [email protected]    (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

✅   [email protected]      (valid)
✅   [email protected]    (valid)
✅   [email protected]     (valid)
✅   [email protected]    (valid, though no TLDs are 1-character long)
✅   [email protected]    (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

✅   [email protected]    (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{
		`[email protected]`,
		`[email protected].`,
		`[email protected]`,
		`emmaly@[email protected]`,
		``,
		`[email protected]`,
		`[email protected]`,
		`emmaly@@example.com`,
		``,
		`"emmaly."@example.com`,
		`".emmaly"@example.com`,
		`"emmaly@"@example.com`,
		``,
		`[email protected]`,
		`[email protected]`,
		`[email protected]`,
		`[email protected]`,
		`[email protected]`,
		``,
		`emmaly@😉.tld`,
		``,
		`[email protected]`,
		``,
		`😉@example.com`,
		``,
		`"😉"@example.com`,
	}

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

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


// false   [email protected]
// false   [email protected].
// false   [email protected]
// false   emmaly@[email protected]
//
// false   [email protected]
// false   [email protected]
// false   emmaly@@example.com
//
// true    "emmaly."@example.com
// true    ".emmaly"@example.com
// true    "emmaly@"@example.com
//
// true    [email protected]
// true    [email protected]
// true    [email protected]
// true    [email protected]
// true    [email protected]
//
// false   emmaly@😉.tld
//
// true    [email protected]
//
// false   😉@example.com
//
// true    "😉"@example.com