fix(email): accept SMTPUTF8 addresses (#11115)

# Which Problems Are Solved

Zitadel only accepted ASCII email addresses, while some users need to
enter internationalized addresses. For example `mö[email protected]`

# How the Problems Are Solved

- Use `net/mail` to validate email addresses, instead of a custom regex.
`net/mail` correctly accepts UTF-8 characters.
- In the management/v1 API email address validation is removed (only
string limits are applied)

# Additional Changes

- none

# Additional Context

Closes https://github.com/zitadel/zitadel/issues/9821

internal/domain/human_email.go

@@ -1,8 +1,9 @@
 package domain
 
 import (
+	"errors"
 	"io"
-	"regexp"
+	"net/mail"
 	"strings"
 	"time"
 
@@ -11,18 +12,20 @@ import (
 	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
-var (
-	emailRegex = regexp.MustCompile("^[a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$")
-)
-
 type EmailAddress string
 
+var errEmailNameProvided = errors.New("email with name provided")
+
 func (e EmailAddress) Validate() error {
 	if e == "" {
 		return zerrors.ThrowInvalidArgument(nil, "EMAIL-spblu", "Errors.User.Email.Empty")
 	}
-	if !emailRegex.MatchString(string(e)) {
-		return zerrors.ThrowInvalidArgument(nil, "EMAIL-599BI", "Errors.User.Email.Invalid")
+	p, err := mail.ParseAddress(string(e))
+	if err != nil {
+		return zerrors.ThrowInvalidArgument(err, "EMAIL-599BI", "Errors.User.Email.Invalid")
+	}
+	if p.Name != "" {
+		return zerrors.ThrowInvalidArgument(errEmailNameProvided, "EMAIL-599GV", "Errors.User.Email.Invalid")
 	}
 	return nil
 }

internal/domain/human_email_test.go

@@ -68,6 +68,20 @@ func TestEmailValid(t *testing.T) {
 			},
 			result: true,
 		},
+		{
+			name: "email UTF-8, valid", // https://github.com/zitadel/zitadel/issues/9821
+			args: args{
+				email: &Email{EmailAddress: "abc@sünde.com"},
+			},
+			result: true,
+		},
+		{
+			name: "email with name, invalid",
+			args: args{
+				email: &Email{EmailAddress: "John Doe <[email protected]>"},
+			},
+			result: false,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {