PDO Overwrite params - php

Question

I've made a simple code to make multiple inserts on the database:
<?php
if (isset($_POST['numb']) && isset($_POST['email1'])) {
$error = false;
$numb = $_POST['numb'];
for ($i = 1; $i <= $numb; $i++) {
if (!isset($_POST['email' . $i])) {
$error = true;
}
}
if ($error == false) {
include 'config.php';
try {
$connection = new PDO($dsn, $user, $pass);
$suc1 = true;
} catch (PDOException $e) {
echo $e->GetMessage();
$suc1 = false;
}
if ($suc1 == true) {
$sql = "INSERT INTO alunos(email, emailKey) VALUES ";
for ($i = 1; $i <= $numb; $i++) {
$BAMBAM[$i] = '(:email' . $i . ', :emailkey' . $i . ')';
$FELIPEFRANCO[$i] = sha1(microtime() . $_POST['email'. $i]);
if ($i != $numb) {
$BAMBAM[$i] = $BAMBAM[$i] . ',';
}
$sql = $sql . $BAMBAM[$i];
}
$insert = $connection->prepare($sql);
for ($i = 1; $i <= $numb; $i++) {
$param1 = 'email' . $i;
$value1 = $_POST['email' . $i];
$param2 = 'emailkey' . $i;
$value2 = $FELIPEFRANCO[$i];
echo '<script>alert("' . $param1 . ' -> ' . $value1 . '")</script>';
$insert->bindParam($param1, $value1, PDO::PARAM_STR);
$insert->bindParam($param2, $value2, PDO::PARAM_STR);
}
try {
$insert->execute();
$suc2 = true;
} catch (PDOException $e) {
echo $e->GetMessage();
$suc2 = false;
}
echo $sql;
} else {
header('Location: addAlunosForm.php?error=internal');
}
} else {
header('Location: addAlunosForm.php?error=fill');
}
} else {
header('Location: addAlunosForm.php?error=fill');
}
?>
There is a test script up there, and, in the alert, it says exactly thiis:
email1 -> 1#gmail.com
email2 -> 2#gmail.com
email3 -> 3#gmail.com
But in the databse, it inserts the 3rd value 3 times:
3
NULL
3#gmail.com
901d4043642394ca30ea83688d944987d266b698
NULL
NULL
4
NULL
3#gmail.com
901d4043642394ca30ea83688d944987d266b698
NULL
NULL
5
NULL
3#gmail.com
901d4043642394ca30ea83688d944987d266b698
NULL
NULL
Details:
$numb is the number of inserts