kataras/iris · error

%s: mx is empty

Error message

%s: mx is empty

What it means

After a successful MX lookup, the ':email' macro requires at least one MX record; an empty result means the domain exists but publishes no mail exchangers, so mail could not be delivered. The library rejects the parameter with this message naming the offending address.

Source

Thrown at macro/macros.go:454

	// Email string type for validating an e-mail path parameter. It returns the address as string, instead of an *mail.Address.
	// It is a combined validation using mail.ParseAddress and net.LookupMX so only valid domains can be passed.
	// It's a more strictly version of the ':mail' path parameter.
	Email = NewMacro("email", "", "", false, false, func(paramValue string) (any, bool) {
		_, err := mail.ParseAddress(paramValue)
		if err != nil {
			return fmt.Errorf("%s: %w", paramValue, err), false
		}

		domainPart := strings.Split(paramValue, "@")[1]

		mx, err := net.LookupMX(domainPart)
		if err != nil {
			return fmt.Errorf("%s: %w", paramValue, err), false
		}

		if len(mx) == 0 {
			return fmt.Errorf("%s: mx is empty", paramValue), false
		}

		return paramValue, true
	})

	simpleDateLayout = "2006/01/02"

	// Date type.
	Date = NewMacro("date", "", time.Time{}, false, true, func(paramValue string) (any, bool) {
		tt, err := time.Parse(simpleDateLayout, paramValue)
		if err != nil {
			return fmt.Errorf("%s: %w", paramValue, err), false
		}

		return tt, true
	})

	// ErrParamNotWeekday is fired when the parameter value is not a form of a time.Weekday.

View on GitHub (pinned to 7bedaf55a0)

Solutions

1. Use a domain that actually publishes MX records if the address must be deliverable.
2. Relax the route to {param:mail} or {param:email}... actually {param:mail} if MX presence should not be required.
3. Verify with `dig MX <domain>` — empty answer section confirms the domain has no MX records.

Example fix

// before
// GET /subscribe/{email:email} with /subscribe/user@domain-without-mx.tld

// after
// GET /subscribe/user@gmail.com  (domain publishes MX records)

mx, err := net.LookupMX(domain); if err == nil && len(mx) == 0 { /* domain has no MX records */ }

func domainAcceptsMail(domain string) bool { mx, err := net.LookupMX(domain); return err == nil && len(mx) > 0 }

When it happens

Trigger: Route {param:email} gets an address whose domain resolves in DNS but has zero MX records (LookupMX returns an empty, non-error slice).

Common situations: Domains that only have A records, parked domains, internal/corporate domains that route mail differently, or freshly registered domains without mail config.

Related errors

• ErrEmptyFormField
• dest directory: %s: eval symlinks: %w
• ErrNotFound
• multipart related: body copy because of iris.Configuration.D
• multipart related: next part: %w

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/b25783244b9e53df. Report an issue: GitHub.