We can do it easily, for example in PHP:
$email = new SendGrid\Email();
$email->addTo('from@abc.com')->
setFrom('to@abc.com')->
setSubject('Subject goes here')->
setText('Hello World!')->
addFilter("subscriptiontrack", "enable", 0)->
addFilter("clicktrack", "enable", 0)->
addFilter("opentrack", "enable", 0)->
addCategory("www")->
setHtml('<strong>Hello World!</strong>');
But for some reasons, Client would like to replay emails to SendGrid by local Postfix and using Drupal built-in mail function without custom code, we can use Postfix smtp_header_checks to add the X-SMTPAPI header for outgoing emails.
Below are steps to do that:
1. Setup Postfix and config it to send emails via SendGrid as here
(it's better to use hashed password file like smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd instead smtp_sasl_password_maps = static:yourSendGridUsername:yourSendGridPassword)
2. Add smtp_header_checks to /etc/postfix/main.cf:
smtp_header_checks = regexp:/etc/postfix/smtp_header_checks
3. Create /etc/postfix/smtp_header_checks file with the content, like:
/^From:/ PREPEND X-SMTPAPI: "category":["www"],"filters":{"subscriptiontrack":{"settings":{"enable":0}},"clicktrack":{"settings":{"enable":0}},"opentrack":{"settings":{"enable":0}}}}
Hint: we can easily get the X-SMTPAPI content by print it out from above PHP code, like:
$arr = $email->toWebFormat();
echo $arr['x-smtpapi'];
4. Reload Postfix
