The common industry term for what you're referring to is "asynchronous bounce" (google it -- it'd help provide more background) and these are actually somewhat uncommon nowadays, as they contribute to a spam/annoyance problem called "backscatter" where somebody other than the sender gets unwanted mail in the form of that delayed bounce. Most big ISPs have moved to methodology where they try very hard to return any NDRs interactively during the initial SMTP delivery attempt to prevent backscatter. In theory, any bounces you'd be seeing like that would be only edge cases, not just common "user unknowns" from most consumer mailbox providers like Microsoft Outlook.com/Hotmail.com.
I haven't heard of Microsoft broadly using async bounce methodology lately. Short answer, not really seeing this in my data and I'd be surprised if it was something Microsoft was moving to-- since it's sort of considered out of date and is one of those things that was a past problem, since mostly solved. Not impossible, but seemingly unlikely. Some broadcast email sending platforms utilize VERP as a way to easily handle asynchronous bounces (see https://en.wikipedia.org/wiki/Variable_envelope_return_path ). But the amount of ISPs using async bounce methodology has reduced over time, it's sort of an open question as to whether or not you would want to bother implementing VERP on a platform that doesn't already have it. And VERP has its own issues, in that spam or junk sent to the VERP address could trigger the sending platform to log a bounce when it shouldn't. Which could result in suppressing mail to an address that isn't actually invalid. And you have to have an inbound email handling process for mail to the VERP bounce address, and if VERP bounce addresses end up on spam lists, you end up pointlessly processing other people's spam, wasting your own CPU cycles. Hope that helps! Feel free to share more details on what you're seeing as desired and we'll see if others on the list have thoughts as well. Cheers, Al Iverson -- Al Iverson // Wombatmail // Chicago Deliverability: https://spamresource.com DNS Tools: https://xnnd.com On Sat, Aug 21, 2021 at 4:53 PM Stuart Hochwert via mailop <mailop@mailop.org> wrote: > > Our tech team has been trying to look more closely into how Microsoft handles > bounces. We are Return Path/Validity Sender Score Certified and have no known > issues. We are a content creator in the arts and crafts and recipe niche > content categories. In looking at an internal write-up it looks like the tech > folks believe Microsoft handles bounces perhaps slightly differently than > other ISP'. Does our review make sense? > > 1 - Microsoft does not appear to immediately bounce the message in the > initial SMTP transaction. > > 2 - We have observed that Microsoft after a delay sends the bounce message > back to the envelope sender. So, we enhanced our bounce processing process to > handle any edge cases. > > But it brought up some internal discussion if this was normal and if this was > a change. Any feedback welcome. Thanks > > --------------------------------------------------- > Stuart Hochwert > shochw...@primecp.com > Prime Publishing LLC > 3400 Dundee Road, Suite 220 > Northbrook, IL 60062 > 847-205-9375 Main | 847-513-6099 Fax | 847-513-6093 Direct > > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
