I'm curious if any of you have heard of a hidden 'quarantine folder' that ISPs rolled out. Supposedly, this folder is for second send emails of the original send, that were re-sent to non-opens with a different subject line. ISPs are identifying these emails based on the HTML being from an already sent email and adding them to this folder the recipient may not see.
Has anyone heard of this? I've searched deliverability blogs and articles to find any information but had no luck. Our client's previous agency told them about the above, and I'm trying to figure out if it's true and what the source was.
Unfortunately I have not heard anything about this either. I know the company Seventh Sense does a lot of work around email deliverability, perhaps they've heard of this if it is in fact true.