Honestly, I don't think you will find an answer to this on the AJO forum either...
When it comes to emails, there is no way to have scripting on an email... scripting in emails was deprecated well over a decade ago due to security issues (sending viruses via email used to be a common thing, so all email readers basically just implemented a complete block of that functionality).
Now, that said, there is no way to determine where the email landed, because there is no script availability... also, I would counter with, not everyone uses those buckets, or may have their own custom buckets for sorting their emails, and even if you could determine the folder, I feel this could constitute a PII issue.
And since Google doesn't disclose the full logic behind their sorting, and could change the logic at any time... I don't know if trying to just create a pseudo logic against the email content would really work.
Are these folders really important? Or is that possibly a grasp at trying to identify email types, without looking at other options?
For example, we have different email types.... now right now, we are just tracking these via campaign code from the links in the emails (we didn't code any noscript tracking embeds into the emails themselves)....
For all emails, we set our medium to "email", but our source will be something like "nl" for newsletter, or "sa" or spotlight author, or we have multiple marketing designations for our marketing emails... and who those emails are targeting.... like is it a subscription driver for registered users, a subscription driver for former subscribers, an engagement / new feature driver for current subscribers, etc....
So instead of trying to classify your emails based on gmail folders (which won't even reflect a lot of users), why not classify your emails based on the type and content of your emails... something that would be consistent no matter what email provider or email reader your users are using....
