Email Local Part Only Regex for Go

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching email local part only, 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 Local Part Only
// ReDoS-safe | RegexVault — Identity & PII > Email Address

package validation

import "regexp"

var emailLocalPartOnlyRe = regexp.MustCompile(`^(?![^@]*\.\.)[a-zA-Z0-9][a-zA-Z0-9._%+\-]{0,62}[a-zA-Z0-9]$|^[a-zA-Z0-9]$`)

func ValidateEmailLocalPartOnly(s string) bool {
    return emailLocalPartOnlyRe.MatchString(s)
}

// Example
// fmt.Println(ValidateEmailLocalPartOnly("user")) // true

Test Cases

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

Technical Notes

Local part max length is 64 chars per RFC 5321. Cannot start or end with a dot. Consecutive dots are prohibited in practice (though technically allowed in quoted strings). Common limit is 64 characters total.