From address doesn't meet the authentication requirements defined for the sender

[#1]

@Townman 
So, if the practice (of innocent use of sub-domains) is prolific, is there widespread chaos or is it only humble Plusnet users who are experiencing rejections from MS (and now Apple)?

[#2]

@abitpedantic
Here's what chatgpt had to say on this matter .

Plusnet appears to be uniquely impacted by these deliverability issues since May/June 2025:

Outgoing mail to Microsoft (Outlook.com / 365) and incoming reception issues emerged around that time across multiple legacy domains (@plus.com, @globalnet, @madasafish).

The root is suspected to involve aggregate authentication failures (SPF, DKIM, DMARC) due to Microsoft treating all *.plus.com senders as a single bulk domain—leading to high rejection or deferral rates .


No similar systemic complaints have appeared for other UK ISPs or domains in the same timeframe

[#3]

@ebforum  If you are going ahead with the migration of your Plusnet email to Greenby could you explain what you mean by saying in your post #445 ...." I will have a large task to migrate all of the places my e-mail address is stored, both for authentication and communication purposes."

If your email address has not changed what action is required?

Like you I have not yet received any personal notification of the migration to Greenby but was aware of what was going on from forum posts back in April. I do not use Plusnet email so will be opting out.

[#4]

@ebforum  I intended to add this link about the migration in my post last night but it wasn't available at the time. You may well have seen it already.

https://www.plus.net/help/email-account-changes/ 

[#5]

Just had this after sending an email to a contact I'd sent to succesfully just yesterday from the same email client...

Reporting-MTA: dns; avasout-ptp-003 [84.93.230.244]
Received-From-MTA: dns; smtpclient.apple [213.1.223.206]
Arrival-Date: Wed, 06 Aug 2025 09:19:40 +0100

Final-recipient: rfc822; info@epic-custom.com
Diagnostic-Code: smtp; 554 5.7.1 ACL dns_rbl; Client host [84.93.230.244] blocked using sa-ip4tset.blagr.emailsrvr.com=127.22.0.2 Senderscore. Please visit https://senderscore.org/rtbl/ for more information on why this message could not be delivered (G31)

[#6]

Just sent a shortish test message to both of my iCloud accounts - both delivered instantly.

[#7]

@jab1, the problem with iCloud accounts, for me, is when I send to an iCloud account and other "non-Microsoft accounts" on one e-mail. So, have you tried to send one e-mail to an iCloud account, a Gmail account and say a btinternet account?

[#8]

@ebforum No, as I said these were both to separate iCloud addresses. I will try a Gmail account as well in the same message, but I've just checked my address book, and I have no contacts left who use BT/MS accounts. The vast majority of my contacts are businesses, who have their own domains.

[#9]

I'll try a combination of my iCloud, Gmail  and yahoo accounts, but it won't  be until later this afternoon.

[#10]

Message sent at 14.18 - almost instant receipt on the iCloud and Yahoo addresses, nothing yet on Gmail.

[#11]

The message arrived in my Gmail inbox at 14.58.

[#12]

Can folks running tests to Gmail please...

1. Look at the SOURCE and note and report the "Delivered after ..." value - for my last two tests they were both 1468 seconds
2. Advise of which email client they were sent from
3. If not webmail, are they on or off the Plusnet network

The SOURCE is easy to look at vial the Gmail webmail interface, no idea what that looks like in other environments.

I find it very odd that two test emails (I have only send two of recent days) should have precisely the same back-off delay applied by Gmail.  I wonder if looking at the Gmail declared back-off delay will provide helpful insight?

[#13]

@Townman I may be thick, or I intentionally don't use Gmail, but I can't see the 'SOURCE' link anywhere.

I sent from Thunderbird on Linux, and off network, obviously, as I'm not a PN subscriber.

For info, the mail was sent at 14.18 and arrived 40 minutes later, at 14.58

[#14]

@jab1 

Hi John - not thick - you have to poke around the UI ... and be given the correct advice!! 🤔

From the Gmail web based UI there is a 'tools' menu behind the stacked three dots ... therein is a SHOW ORIGINAL option which exposes the email SOURCE.  Wherein...

Hope that clarifies!!

[#15]

It does, thanks @Townman  says: Delivered after 2379 seconds.  39.65 minutes