XF 2.2 SMTP Email Header Question

[xlegends]

Hello,

I use smtp relay to sendgrid and it works great. I have a large aging forum. Today, I used an email validation service to build a list of thousands of bad emails. You can upload a supression or do-not send list at sendgrid but apparently it only works if you are sending marketing emails from their console directly.

Emails coming from the forum's smtp-relay do not check the custom uploaded do not send supression lists.


Unless you add one of these Web API v2/Web API v3 supported code to the email header

{
  "asm_group_id": 1
}

or

{
  "asm_groups_to_display": [1, 2, 3]
}

So my question is, which template can I edit this into the email header?