add check in split for missing @ to avoid panic

Author: agau4779

checkmail.go

@@ -117,6 +117,10 @@ func DialTimeout(addr string, timeout time.Duration) (*smtp.Client, error) {
 
 func split(email string) (account, host string) {
 	i := strings.LastIndexByte(email, '@')
+	// If no @ present, not a valid email.
+	if i < 0 {
+		return
+	}
 	account = email[:i]
 	host = email[i+1:]
 	return

checkmail_test.go

@@ -27,6 +27,7 @@ var (
 		{mail: "é&ààà@gmail.com", format: false, account: false},
 		{mail: "[email protected]", format: true, account: false},
 		{mail: "[email protected]", format: true, account: false},
+		{mail: "", format: false, account: false},
 	}
 )