<?php

$myArray = [
  ['email' => 'email1@email.com', 'value' => 'aaa'],
  ['email' => 'email1@email.com', 'value' => 'bbb'],
  ['email' => 'email1@email.com', 'value' => 'ccc'],
  ['email' => 'email2@email2.com', 'value' => 'ddd'],
  ['email' => 'email2@email2.com', 'value' => 'eee']
];

foreach ($myArray as $item) {
	$newArray[$item['email']][] = $item['value'];
}

var_dump($newArray);