Find the column value of the first item in a multidimensional array with a sought value in a deep subarray

I am creating a contact form, which needs to change the sendto address based on an entered postal code.

I have an array of postal codes which I can search through, so that I know if the postal code entered is actually in the array.

Here's how I search through the array:

$districts = [
    'district' => [
        [
            'name' => 'District A',
            'email' => 'abc@example.com',
            'url' => 'district-a',
            'postalcodes' => [
                '3311AA',
                '3311AB',
            ],
        ],
        [
            'name' => 'District B',
            'email' => 'xyz@example.com',
            'url' => 'district-b',
            'postalcodes' => [
                '3317EA',
                '3317EB',
                '3317EC',
            ],
        ],
    ],
];

$results = array_filter($districts['district'], function($district) {
    $key = array_search('3311AB', $district['postalcodes']);
    return $key;
});

var_dump($results);

Now I need to return the email address, based on in which district the postal code is found.

How would I search for, for example, postal code 3311AB and return the email address of the district to which it belongs?

Instead of returning key of postal code, you need to return $district['email']

$emails = [];

foreach ($districts['district'] as $district) {
    if (in_array('3311AB', $district['postalcodes'])) {
        $emails[] = $district['email'];
    }
}

var_dump($emails);

Example