Update of Magento's Ashroder Email module's lib/AmazonSES.php file to work with Signature version 4.

app_code_local_Aschroder_Email_lib_AmazonSES.php

<?php

/**
 * Zend_Http_Client extended for a function to sign a request for AmazonSES with signature version 4.
 *
 * @author jEzEk - 20210222
 */
class Zend_Http_Client_AmazonSES_SV4 extends Zend_Http_Client {

	  const HASH_ALGORITHM = 'sha256';
		public static $SESAlgorithms = [
			self::HASH_ALGORITHM => 'AWS4-HMAC-SHA256',
		];

    /**
     * Returns header string containing encoded authentication key needed for signature version 4 as described in https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html
     * 
		 * @param DateTime $date
		 * @param string $region
		 * @param string $service
		 * @param string $accessKey
		 * @param string $privateKey
		 * @return  string
		 *
     */
    public function buildAuthKey(DateTime $date, $region, $service, $accessKey, $privateKey){
			//Mage::log(__METHOD__);
			$longDate = $date->format('Ymd\THis\Z');
			$shortDate = $date->format('Ymd');

			// Add minimal headers
			$this->setHeaders([
				'Host' => $this->uri->getHost(),
			  'X-Amz-Date' => $longDate,
		 	]);

			// Task 1: Create a canonical request for Signature Version 4
			// 1. Start with the HTTP request method (GET, PUT, POST, etc.), followed by a newline character.
			$method = $this->method . "\n";

			// 2. Add the canonical URI parameter, followed by a newline character
			$canonicalUri = $this->pathEncode($this->uri->getPath()) . "\n";

			// 3. Add the canonical query string, followed by a newline character. 
			$canonicalQuery = $this->getQuery() . "\n";

			// 4. Add the canonical headers, followed by a newline character. 
			$canonicalHeaders = "";
			$headers = $this->headers;
			ksort($headers, SORT_STRING);
			foreach ($headers as $k => $v) {
				$canonicalHeaders .= $k . ':' . $this->trimAllSpaces($v[1]) . "\n";
			}
			$canonicalHeaders .= "\n";

			// 5. Add the signed headers, followed by a newline character.
			$signedHeaders = implode(';', array_keys($headers)) . "\n";

			// 6. Use a hash (digest) function like SHA256 to create a hashed value from the payload in the body of the HTTP or HTTPS request. 
			$hashedPayload = $this->hash($this->_prepareBody());

			// 7. To construct the finished canonical request, combine all the components from each step as a single string.
			$canonicalRequest = $method . $canonicalUri . $canonicalQuery . $canonicalHeaders . $signedHeaders . $hashedPayload;

			//Mage::log('canonicalRequest:');
			//Mage::log("#####\n" . $canonicalRequest . "\n#####");

			// 8. Create a digest (hash) of the canonical request with the same algorithm that you used to hash the payload.
			$hashedCanonicalRequest = $this->hash($canonicalRequest);

			// Task 2: 
			// 1. Start with the algorithm designation, followed by a newline character.
			$algorithm = self::$SESAlgorithms[self::HASH_ALGORITHM] . "\n";

			// 2. Append the request date value, followed by a newline character.
			$requestDateTime = $longDate . "\n";

			// 3. Append the credential scope value, followed by a newline character. 
			$credentialScope = $shortDate . '/' .$region. '/' .$service. '/aws4_request' . "\n";

			// 4. Append the hash of the canonical request that you created in Task 1: Create a canonical request for Signature Version 4. 
			$stringToSign = $algorithm . $requestDateTime . $credentialScope . $hashedCanonicalRequest;
			
			//Mage::log('stringToSign:');
			//Mage::log("#####\n" . $stringToSign . "\n#####");

			// Task 3: Calculate the signature for AWS Signature Version 4
			// 1. Derive your signing key. 
			$dateKey = hash_hmac(self::HASH_ALGORITHM, $shortDate, 'AWS4' . $privateKey, true);
			$regionKey = hash_hmac(self::HASH_ALGORITHM, $region, $dateKey, true);
			$serviceKey = hash_hmac(self::HASH_ALGORITHM, $service, $regionKey, true);
			$signingKey = hash_hmac(self::HASH_ALGORITHM, 'aws4_request', $serviceKey, true);

			// 2. Calculate the signature.
			$signature = hash_hmac(self::HASH_ALGORITHM, $stringToSign, $signingKey);

			// Task 4: Add the signature to the HTTP request
			// Return string for HTTP Authorization header
			return trim($algorithm, "\n") . ' Credential=' . $accessKey . '/' . trim($credentialScope, "\n") . ', SignedHeaders=' . trim($signedHeaders, "\n") . ', Signature=' . $signature;
    }

		protected function pathEncode($path) {
			$encoded = [];
			foreach (explode('/', $path) as $k => $v) {
				$encoded[] = rawurlencode(rawurlencode($v));
			}
			return implode('/', $encoded);
		}

		protected function trimAllSpaces($text) {
			return trim(preg_replace('| +|', ' ', $text), ' ');
		}

		protected function hash($text) {
			return hash(self::HASH_ALGORITHM, $text);
		}

		protected function getQuery() {
			// From Zend_Http_Client:L946
			// Clone the URI and add the additional GET parameters to it
			$uri = clone $this->uri;
			if (! empty($this->paramsGet)) {
				$query = $uri->getQuery();
				if (! empty($query)) {
					$query .= '&';
				}
				$query .= http_build_query($this->paramsGet, null, '&');
				if ($this->config['rfc3986_strict']) {
					$query = str_replace('+', '%20', $query);
				}

				$uri->setQuery($query);
			}
			return $uri->getQuery();
		}
}

/**
 * Amazon Simple Email Service (SES) connection object
 *
 * Integration between Zend Framework and Amazon Simple Email Service
 *
 * @category    Zend
 * @package     Zend_Mail
 * @subpackage  Transport
 * @author      Christopher Valles <info@christophervalles.com>
 * @license     http://framework.zend.com/license/new-bsd New BSD License
 */
class App_Mail_Transport_AmazonSES extends Zend_Mail_Transport_Abstract
{
    /**
     * Template of the webservice body request
     *
     * @var string
     */
    protected $_bodyRequestTemplate = 'Action=SendRawEmail&Source=%s&%s&RawMessage.Data=%s';


    /**
     * Remote smtp hostname or i.p.
     *
     * @var string
     */
    protected $_host;


    /**
     * Amazon Access Key
     *
     * @var string|null
     */
    protected $_accessKey;


    /**
     * Amazon private key
     *
     * @var string|null
     */
    protected $_privateKey;

    /**
     * Amazon region endpoint
     *
     * @var string|null
     */
    protected $_region;

    private $endpoints = array(
        'US-EAST-1' => 'email.us-east-1.amazonaws.com',
        'US-WEST-2' => 'email.us-west-2.amazonaws.com',
        'EU-WEST-1' => 'email.eu-west-1.amazonaws.com',
        'EU-CENTRAL-1' => 'email.eu-central-1.amazonaws.com',
    );


    /**
     * Constructor.
     *
     * @param  array|null $config (Default: null)
     * @param  string $host (Default: https://email.us-east-1.amazonaws.com)
     * @return void
     * @throws Zend_Mail_Transport_Exception if accessKey is not present in the config
     * @throws Zend_Mail_Transport_Exception if privateKey is not present in the config
     */
    public function __construct(Array $config = array(), $region = 'US-EAST-1')
    {
        if(!array_key_exists('accessKey', $config)){
            throw new Zend_Mail_Transport_Exception('This transport requires the Amazon access key');
        }
        
        if(!array_key_exists('privateKey', $config)){
            throw new Zend_Mail_Transport_Exception('This transport requires the Amazon private key');
        }
        
        $this->_accessKey = $config['accessKey'];
        $this->_privateKey = $config['privateKey'];
				$this->_region = $region;
        $this->setRegion($region);
    }

    public function setRegion($region) {
        if(!isset($this->endpoints[$region])) {
            throw new InvalidArgumentException('Region unrecognised');
        }
        return $this->_host = Zend_Uri::factory("https://" . $this->endpoints[$region]);
    }

    /**
     * Send an email using the amazon webservice api
     *
     * @return void
     */
    public function _sendMail()
    {
        //Build the parameters
        $params = array(
            'Action' => 'SendRawEmail',
            'Source' => $this->_mail->getFrom(),
            'RawMessage.Data' => base64_encode(sprintf("%s\n%s\n", $this->header, $this->body))
        );
        $recipients = explode(',', $this->recipients);
        while(list($index, $recipient) = each($recipients)){
            $params[sprintf('Destinations.member.%d', $index + 1)] = $recipient;
        }

        // Create client
        $client = new Zend_Http_Client_AmazonSES_SV4($this->_host);
        $client->setMethod(Zend_Http_Client::POST);
        $client->setParameterPost($params);
        
	// Add authorization header
        $client->setHeaders(array(
            'Authorization' => $client->buildAuthKey(new DateTime('NOW'), strtolower($this->_region), 'email', $this->_accessKey, $this->_privateKey)
        ));

	// Send request
        $response = $client->request(Zend_Http_Client::POST);
        
        if($response->getStatus() != 200){
            throw new Exception($response->getBody());
        }
    }

    public function getSendStats()
    {
        //Build the parameters
        $params = array(
            'Action' => 'GetSendStatistics'
        );

	// Create client
        $client = new Zend_Http_Client_AmazonSES_SV4($this->_host);
        $client->setMethod(Zend_Http_Client::POST);
        $client->setParameterPost($params);

        // hhvm Invalid chunk size fix - force HTTP 1.0
        $client->setConfig(array(
          'httpversion' => Zend_Http_Client::HTTP_0,
        ));
        // -----
				
	// Add authorization header
        $client->setHeaders(array(
            'Authorization' => $client->buildAuthKey(new DateTime('NOW'), strtolower($this->_region), 'email', $this->_accessKey, $this->_privateKey)
        ));

	// Send request
        $response = $client->request(Zend_Http_Client::POST);

        if($response->getStatus() != 200){
            throw new Exception($response->getBody());
        }

        return $response->getBody();
    }


    /**
     * Format and fix headers
     *
     * Some SMTP servers do not strip BCC headers. Most clients do it themselves as do we.
     *
     * @access  protected
     * @param   array $headers
     * @return  void
     * @throws  Zend_Transport_Exception
     */
    protected function _prepareHeaders($headers)
    {
        if (!$this->_mail) {
            /**
             * @see Zend_Mail_Transport_Exception
             */
            throw new Zend_Mail_Transport_Exception('_prepareHeaders requires a registered Zend_Mail object');
        }
        
        unset($headers['Bcc']);
        
        // Prepare headers
        parent::_prepareHeaders($headers);
    }


    /**
     * Returns header string containing encoded authentication key
     * 
     * @param   date $date
     * @return  string
     */
    private function _buildAuthKey($date){
        return sprintf('AWS3-HTTPS AWSAccessKeyId=%s,Algorithm=HmacSHA256,Signature=%s', $this->_accessKey, base64_encode(hash_hmac('sha256', $date, $this->_privateKey, TRUE)));
    }
}

well done, much appreciated.

Thanks a lot for the working code! AWS kill brains with their official docs as usuall!
Thx one more time)

Maybe this was written with a slightly different version to ours. Was seeing Region unrecognised exception

I had to make this change

class Aschroder_SMTPPro_Model_Transports_Ses {


    public function getTransport($storeId) {

        $_helper = Mage::helper('smtppro'); /* @var $_helper Aschroder_SMTPPro_Helper_Data */
        $_helper->log("Getting Amazon SES Transport");

        $path = Mage::getModuleDir('', 'Aschroder_SMTPPro');
        include_once $path . '/lib/AmazonSES.php';

        $emailTransport = new App_Mail_Transport_AmazonSES(
            array(
                'accessKey' => $_helper->getAmazonSESAccessKey($storeId),
                'privateKey' => $_helper->getAmazonSESPrivateKey($storeId)
            ),
            'https://email.'.$_helper->getAmazonSESRegion($storeId).'.amazonaws.com',
            $_helper->getAmazonSESRegion($storeId)
        );

        return $emailTransport;
    }
}

And tweak App_Mail_Transport_AmazonSES

    /**
     * Amazon Access Key
     *
     * @var string|null
     */
    protected $_accessKey;

    /**
     * Amazon private key
     *
     * @var string|null
     */
    protected $_privateKey;

    /**
     * Amazon region endpoint
     *
     * @var string|null
     */
    protected $_region;

    private $endpoints = array(
        'us-east-1' => 'email.us-east-1.amazonaws.com',
        'us-west-2' => 'email.us-west-2.amazonaws.com',
        'eu-west-1' => 'email.eu-west-1.amazonaws.com',
        'eu-central-1' => 'email.eu-central-1.amazonaws.com',
    );

    /**
     * Constructor.
     *
     * @param  array|null $config (Default: null)
     * @param  string $host (Default: https://email.eu-west-1.amazonaws.com)
     * @param  string $region (Default: us-east-1)
     * @return void
     * @throws Zend_Mail_Transport_Exception if accessKey is not present in the config
     * @throws Zend_Mail_Transport_Exception if privateKey is not present in the config
     */
    public function __construct(Array $config = array(), $host = 'https://email.eu-west-1.amazonaws.com', $region = 'eu-west-1')
    {
        [...]

Hi @jezek,
I am also getting the Region Unrecognized error. Could you or @DominicWatts elaborate on how to fix this issue? That would be greatly appreciated.

Thank you for your time.

@tomakun I'm really sorry. I did this work for some guy and for him it's working. I don't have time, nor motivation to fix your problem. You're on your own. Happy hacking, I hope you solve your problem. If you solve it, don't forget to post your solution. ;)

@Jazek

I posted the two changes I needed to make

It's the endpoints and the constructor argument

@jezek @DominicWatts and to anybody getting the Region Unrecognized issue, in the end I was able to make it work with using ONLY @jezek 's file above - Here's how:

You need to make sure you are running the latest version of the Aschroder SMTP Pro plugin before replacing the lib/AmazonSES.php file provided by @jezek above.

Once you are up to date and using @jezek's file above, run a self test from the plugin's Logging and Debugging panel in the Magento dashboard. From the self test, if you get a "Email address not verified" "Check if you email address is verified and SES region" error, you will need to update line 206:

public function __construct(Array $config = array(), $region = 'US-EAST-1')

and change US-EAST-1 to whatever region you are using in SES. In my case I had to change it to US-WEST-2. The next self test was successful, all emails being sent without issues.

Thank you @jezek for this Gist.

@tomakun Good work and thank you for additional info for all future visitors.