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

[#1]

@Townman 

Thanks for your recent posts and attempts to summarise the situation.  Most timely.

However you write  "Unless I have missed something, the only current reports relate to sending the same email to multiple recipients across more than one Microsoft brand.  Send to one recipient or one brand and there are no issues."

My experience is that sending an email to a single MS-related address works OK but that adding any second recipient to the address list will cause the MS address to fail.  The second recipient may or may not be MS-related.  Eg an email to only a Hotmail and a Btinternet address will cause the Hotmail address to fail.

Does this help?

[#2]

@Tim-J 

If these were failing on spam threshold (SCL=6) I would agree, but they are not - the bonce back is a DKIM failure. 

[#3]

@Silver-Codger 

Yes - very much so - thank you.  Are you encountering this only with Hotmail?  I have not found issue with Outlook and Gmail.

I can see that I might need to get a fist full of new redundant email accounts live / hotmail / icloud ... !!

[#4]

@PhilipHeyes "For us it is emails with multiple destinations where there is one or more Microsoft destination(s)
the one or more MS email a/c will each be rejected."

I've had an email to a group of 8 or 9 contacts where Outlook.com bounced but Hotmail didn't.

Then another day, for an email to the same group of contacts, Hotmail bounced but Outlook.com didn't.

This is a reason why I suspect spam filtering, giving seemingly random outcomes.  But with an underlying high points score caused by the DKIM issue, which may then be toppled over the edge by something else.

[#5]

Tim,

Do you have the NDR reports still?

What do they indicate - suspected SPAM or DKIM failure?  If the latter, is there any detail, such as 'lookup timeout'?

Which Plusnet AVSOUT did they pass through?

[#6]

@Townman If these were failing on spam threshold (SCL=6) I would agree, but they are not - the bonce back is a DKIM failure. 

My suggestion (which may be wrong) is that the DKIM failure is a contributor to the spam threshold.  Are you sure that we're not getting both together?

[#7]

For us if we send a business email to say 5 destinations - where there is 1 MS destination I see 1 DKIM=FAIL rejection & 4 emails delivered.

For us if we send a business email to say 5 destinations - where there are 3 MS destination I see 3 DKIM=FAIL rejections and 2 emails delivered.

We have come to expect a 100% failure rate to MS in multi destination emails.

We see sporadic rejections from Apple icloud but appear to only have 1 trustee on that email platform.

At present emails are being delivered to GMAIL.

Most recently avasout-ptp-003 [84.93.230.244] has been rejected once by outlook.com and by twice by talktalk.com

[#8]

@Townman Do you have the NDR reports still?

I'll see if I can find them, but possibly not immediately.

[#9]

@Townman 

You asked "Are you encountering this only with Hotmail?"

Due to the small size of my address book the only MS-related addresses I have attempted to send to have been Hotmail. Without pestering other people i don't know very well it would be difficult to get test results for, say, Outlook.com recipients.  My other reservation and reason I have not pushed further diagnosics on this thread is that I am still using Outlook 2010 as my email client and you will be aware that Microsoft stopped supporting this in October 2020 .

Keep up the good work!

[#10]

@PhilipHeyes 

If you send a business email to say 5 destinations - where all are a MS destination - what do you see?

[#11]

Sending an email to 5 MS destination is a test for Plusnet to perform from MS Outlook.

Set up some test a/c on live / outlook / hotmail etc


Customer emails from multiple trustee bodies can't be used for such a test.

[#12]

Not quite the requested test but business email attempted to 7 destinations and sending server shown as :

Reporting-MTA: dns; avasout-ptp-003 [84.93.230.244]

Delivered only to yahoo.com & btopenworld.com

Rejected by: msn.com  /  hotmail.com / outlook.com  all with : Spf= Pass , Dkim= Fail , DMARC= Pass 

Rejected by: talktalk.net with :

Final-recipient: rfc822; xxxxxxxzyk@talktalk.net
Diagnostic-Code: smtp; 550 5.7.1 Connection refused - [84.93.230.244] blocked by Validity - https://senderscore.org/blocklist-lookup/ - OXSEU001_102 - https://postmaster-oxseu.vadesecure.com/inbound_error_codes/#_102

[#13]

@Townman 

What did you make of my post #473 - is DMARC=Fail significant?

By the way, I don’t know the composition of the group named ‘xxxx’ but each of the half a dozen rejections that I got from postmaster@outlook.com provided me with the email address of the failed recipient (all hotmail or outlook).

Also of possible interest, I sent an email at the weekend from MS Outlook to 3 recipients (1 hotmail and 2 btinternet) and was surprised to receive no rejections - must be fine margins.

P.S. In amongst the virtually incomprehensible failure blurb, I spotted “dkim=timeout (key query timeout)” and
“Received: from avasout-peh-002.plus.net (212.159.14.18)”.

[#14]

The reality is a 71% delivery failure rate on a single business email is an utterly shameful outcome.

It is now not just Microsoft.

It is talktalk.net too that have in the exact same way rejected the same server's IP 3 times in a week.

I am totally struggling to find any kind words !   The SMTP reputation is utterly merde.


Earlier in the day or yesterday it was mentioned about a curiosity of why domestic email sender's platform sent > 5000 emails to MS email accounts.   I initialled ignored this as being not my concern.

But is it case there are spam or bulk senders on the platform ?

Or is that a case of Plusnet has over 500,000 email accounts and that means only
1% of customers sending an email per day to a Microsoft account amounts 5000 emails ?

[#15]

Getting this message in the bounce detail

host eur.olc.protection.outlook.com [52.101.73.29]
SMTP error from remote mail server after end of data:
550 5.7.515 Access denied, sending domain MEGAPOWER.PLUS.COM doesn't meet the required authentication level. The sender's domain in the 5322.From address doesn't meet the authentication requirements defined for the sender. To learn how to fix this see:
https://go.microsoft.com/fwlink/p/?linkid=2319303 Spf= Pass , Dkim= Pass , DMARC= Fail [GV2P192MB2592.EURP192.PROD.OUTLOOK.COM 2025-08-13T16:42:19.169Z 08DDD9FF8AE03ED8] [CWLP265CA0495.GBRP265.PROD.OUTLOOK.COM 2025-08-13T16:42:19.197Z 08DDDA1820CD8854] [AMS0EPF000001B4.eurprd05.prod.outlook.com 2025-08-13T16:42:19.210Z 08DDD95E26B6BAE6]

I'm sending from outlook but am no longer using relay.plus.net to send as not only did emails to the account that boiunced this bounce but Outlook then stopped sending any emails at all.