While these factors can cause a quarantine or even silent disposal, empirical evidence suggests that there are custom mechanisms (ie spam filters) downstream th

While these factors can cause a quarantine or even silent disposal, empirical evidence suggests that there are custom mechanisms (ie spam filters) downstream that do the larger part of the filtering. I have been running private Mail servers since the early 2000s and this last decade has certainly not been nice to folks that want to self host. I cannot even send my mother in law email because Google just plainly denies delivery with no way to circumvent. Funnily enough mass mailing from the same account 10000 other gmail addresses has delivery metrics just like doing it with mailchimp. I think it is safe to say that big email hosting has grown so complex internally that the companies themselves can’t really make sense of it any more. Edit: to preempt possible “you are doing it wrong” comments, my Mail server setup checks out in every conceivable test suite and email content as well :-)