Email Address (RFC 5321 Practical) Regex for Go
/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\.[a-zA-Z]{2,}$/iWhat this pattern does
This page provides a comprehensive, battle-tested regular expression for matching email address (rfc 5321 practical), ported and verified for Go. Identity and credential patterns need both correctness and safety, since they're frequent targets for adversarial input. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.
Go Implementation
// Email Address (RFC 5321 Practical)
// ReDoS-safe | RegexVault — Identity & PII > Email Address
package validation
import "regexp"
var emailAddressRfc5321PracticalRe = regexp.MustCompile(`^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*\.[a-zA-Z]{2,}$`)
func ValidateEmailAddressRfc5321Practical(s string) bool {
return emailAddressRfc5321PracticalRe.MatchString(s)
}
// Example
// fmt.Println(ValidateEmailAddressRfc5321Practical("user@example.com")) // trueTest Cases
Matches (Valid) | Rejects (Invalid) |
|---|---|
user@example.com | @example.com |
user.name+tag@example.co.uk | user@ |
user@sub.domain.com | user@.com |
x@y.io | user@@example.com |
test123@test.co | user@exam_ple.com |
| — | user@com |
When to use this pattern
This pattern is drawn from the Identity & PII > Email Address category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.
Common Pitfalls
Full RFC 5321 compliance allows addresses like '"user name"@example.com' and 'user@[192.168.1.1]' — valid technically but rejected by nearly all mail servers. Practical patterns are more useful than RFC-complete ones.
Technical Notes
Deliberately excludes quoted strings and IP address literals (RFC 5321 allows them but they are vanishingly rare in practice). The TLD must be at least 2 letters. Internationalized domain names (IDN) require Punycode encoding first.
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