@revk @neil Interestingly that puts people who use intermediary services like Mimecast at a disadvantage compared to those who just publish the M365 MX records. The company I work for is in this situation, with the mail then backing up at Mimecast. The tests I sent this morning seem to indicate that MS are responding with 4XX temp failure codes on the SMTP level.
@andrew @revk @neil It's not that unusual to how some big financial companies handle mail - many use a physical mail processing company to receive the mail and I guess scan and forward it electronically. It's fairly easy to spot when you notice the postcode for big companies is all neighbouring ones in the same town where the company isn't.
Nov 13, 2026, 2:51 PM@penguin42 @andrew @neil I would not say a disadvantage but a clear demarkation of responsibility.
If you contract with someone to handle your email sending (e.g. ISP) the demarkation is when they send it on to the MX of the recipient. You chose to contract out your sending.
But if someone contracts out their receiving, which, as you say, happens, the recipient is taking responsibility as they are the ones that contacted that out.
You need a line, and handed to an MX for domain is a good one
Nov 13, 2026, 2:56 PM@penguin42 @andrew @neil My key issue here is that there should be a specific point that sender hands over responsibility to recipient.
Up to then, any failure is the sender's fault.
Beyond that is the recipient's fault.
Contracting someone else for each side does not change that reality.
As I say, there is always some technical edge cases on that specific SMTP connection, which is unavoidable but really not going to happen in most cases.
This also fixes the date/time.
Nov 13, 2026, 3:00 PM@penguin42 @andrew @neil This is not unlike postal service.
I suspect the demarcation is putting the letter in the post box. The timestamp is the postmark (when they existed).
@revk @andrew @neil Well you can get 'proof of posting' at a post-office; and often you're told to use tracked/signed-for - so there's some requirement on the sender to do something in the face of a delivery system that's known to be flaky.
(which in the case of mail handling companies is useless - you get a delivery picture of a huge box sitting on a table without your letter visible)
Nov 13, 2026, 3:05 PM@penguin42 @andrew @neil Ha, yeah, but for some legal things a "proof of posting" is all you need. My suggestion on MX of recipient domain is actually a tad further down the line, but also allows for people sending email themselves not using an ISP.
I have had such a picture (to amazon) and sued RM (who caved) on basis proof of delivery picture did not show *my* package (distinctive colour even).
Nov 13, 2026, 3:06 PM@revk @penguin42 @andrew @neil iirc with Royal Mail there is (in the context of legal notices) a presumption of delivery - if you can prove postage then it's on the other party to prove that it wasn't delivered. I don't know if there's anything analogous in email
Nov 13, 2026, 3:18 PM@dan @penguin42 @andrew @neil I think the discussion here is maybe we can establish some similar ground rules for email.
@revk @penguin42 @andrew @neil No the postal service is special here
You have an interest in proving and email was or was not delivered. You can tamper with or lose your server logs. Stuff can get lost. SMTP is not reliable
The post office is notionally an uninterested third party with a process in place to manage high reliability document delivery and recognized as such.
The analogy would be not using email but both using an agreed reliable third party provider of electronic document service
Nov 13, 2026, 3:21 PM@etchedpixels @revk @penguin42 @andrew @neil
While technically true, recent event have seen 1st class mail here be delivered in the 3rd week after it was posted and the new barcodes on the side of stamps mean they are not franked with the posing date (I assume the PO can look up in DB the day/time it was scanned, but it's harder to verify)
Nov 13, 2026, 3:23 PM@etchedpixels @penguin42 @andrew @neil SO by that logic, contracting sending to an uninterested 3rd party ISP who can provide email logs of attempted or actual delivery, creates the same logic.
@revk @etchedpixels @penguin42 @neil I struggle to see how you can do this via email to be honest. In most cases especially with the third party companies involved these days there are too many points of failures and wiggle room.
Nov 13, 2026, 8:06 PM@andrew @etchedpixels @penguin42 @neil there are surely parties contracted by sender and parties contracted by recipient?
Nov 13, 2026, 6:48 PM@etchedpixels @revk @penguin42 @andrew @neil presenting tampered logs in court would, of course, be contempt, so would be quite a risk