Invalid MSGID (RFC 2822)

The Message-Id is not following the RFC 2822. That affects SpamAssassin score negatively and might even get emails marked as spam.

Solution:

/Postman/PostmanWpMail.php line 87:

– return $id . '@' . str_replace('www.', '', $hostName);
+ return '<' . $id . '@' . str_replace('www.', '', $hostName) . '>';

The issue has been opened earlier but seems staled and closed.

During a deliverable test, I noticed that I was getting the error INVALID_MSGID Message-Id is not valid, according to RFC 2822for emails sent using SMTP Mail Mailer / Email Login + SendGrid API. This was actually lowering SpamAssassin’s score, which led to the email being considered spam.

The problem seems to be that the Message-IDangle brackets are missing from the header around its value, eg. Message-ID: abc@def.com instead of Message-ID: <abc@def.com>. Once I created the tiny array below, I stopped getting the error.

https://wordpress.org/support/topic/invalid-msgid/#post-14671322