php - Swiftmailer DKIM fails only with multipart email -

i'm attempting dkim working swiftmailer php. works , dkim passes when setting body once (html or text), when adding both parts "body hash did not verify" dkim fail.

does know correct way sign email both html , text parts using swiftmailer?

// create signer     $privatekey = file_get_contents($dkimprivatekeylocation); $domainname = 'from.here'; $selector = 'default'; $signer = new swift_signers_dkimsigner($privatekey, $domainname, $selector); $signer->ignoreheader('return-path');  // create message $message = swift_signedmessage::newinstance();                    // attach signer $message->attachsigner($signer);  // message setup $message->setfrom('email@from.here'); $message->setto('email@to.here'); 

html passes

$message->setsubject('dkim html test'); $message->setbody('<p>hello world</p>', 'text/html','utf-8');  

text passes

$message->setsubject('dkim text test'); $message->setbody('hello world', 'text/plain','utf-8'); 

html , text fails

$message->setsubject('dkim html , text test'); $message->setbody('<p>hello world</p>', 'text/html','utf-8');  $message->addpart('hello world', 'text/plain','utf-8'); 

i'm not sure i'm doing wrong, swiftmailer documentation little sparse i'm not sure try next. have tried both simple , relaxed types body canon no success.