How to set up FBL Gmail?

Question

gmail

I read the instructions https://support.google.com/mail/answer/6254652
Something I can’t understand what exactly to pass in the header and using php should I set the header when sending, or should I configure it on the server side?
Feedback-ID: CampaignIDX:CustomerID2:MailTypeID3:SenderId
SenderId is clear, but what should I write about the first 3?

Answer 1

Something I can’t understand what exactly to pass in the header and with the help of php you need to set the header when sending, or do you need to configure it on the server side?

That's right, it's a normal postal email header. So indicate:
Feedback-ID: [xxx]:[yyy]:[zzz]:[unique_code].
You need to configure it where the sending comes from. How do you do it? Vanga is not here, unfortunately.
As far as I understand, this is an analogue of the usual UTM tag, only for the purposes of tracking those who are dissatisfied with the campaign. Accordingly, the first three parameters - you write correctly. The last parameter is SenderIdany unique code, from 5 to 15 characters long, for example like this - GB8taFNHZM .