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

[#1]

This is just our normal day job of emailing to a small groups of people so they can use Reply All to give feedback and see each other comments.

Does sending via port 465 vs 587 make any difference ?

I have always favoured using 465 as this ensures encryption is used
where as for 587 encryption may be optional.

[#2]

Should not, that is just the connection to the server.

The use of port 465 is though deprecated.

[#3]

Good Afternoon,

We have a new support ticket open to investigate the issue you're seeing when sending an email to multiple recipients.

I've updated the service information post - Sending emails to Microsoft-owned domains such as ... - Plusnet Community - and will post any updates I receive there.

Thanks to all who have reported this issue.

James

[#4]

I have tried sending from webmail to multiple addresses and all were successfully sent. This made me wonder whether it was the Outlook desktop client that was the issue. To test this I installed Thunderbird and sent from there with same settings I use in Outlook. This was also successfully sent. Not sure what that means or why it should make a difference.

[#5]

Responding to the comments about MS Outlook being a suspect in this issue.

Using the same retail HP Laptop with Windows 11 and using an installed version of MS Outlook ( current subscription ) what for us consistently rejects with DKIM Failure via Plusnet works perfectly if sent via a 123Reg email a/c.

It is not possible for us to just swop sending email a/c because that is not what the clients expect to see
especially as the 123Reg email and domain belong to a different business.

[#6]

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@PhilipHeyes wrote:

We have MS Outlook and use distribution lists to address the Trustees of a charity, 3 emails are Microsoft accounts.  
Sending messages using the distribution list resuts in immediate bounce messages from each Microsoft email address.

whenever a distribution list contains multiple Microsoft email addresses each MS email fails.

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Sometimes problem descriptions need to be read and reread before a clue emerges.  My tests simply sent an email to an outlook address and a hotmail or live email address.  My tests did not send via a distribution list!

What distribution list are you using - or is that just a turn of phrase for having a list of emails which you paste into the TO field?  Have you tried to send an email to just the three addresses together, not using an intermediary distribution list?

With the unclear difficulties created by Microsoft with the muddled changes, one has to consider that there is a possibility that the use of a distribution list without a link to unsubscribe for said list, is what is giving rise to the failure here.

There are various commentaries on if UNSUBSCIRBE links are mandatory or just recommended for bulk senders and there-in becomes the issue - if *.plus.com id deemed a single bulk sender ... anyone using a distribution list might be blighted by even more unclear requirements.

More information: sight of some of the results X headers might be informative (SCL / BCL) and the detail of the DKIM look-up - it is one thing to show the failure report but what is in the failure diagnostic?

[#7]

@Townman @MisterW @James_B It seems that I can replicate @rbb99's experience:

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@rbb99 wrote:

... whether it was the Outlook desktop client that was the issue. To test this I installed Thunderbird and sent from there with same settings I use in Outlook. This was also successfully sent. Not sure what that means or why it should make a difference.

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My usual email client is Outlook 2016 (from the Office 2016 Professional Plus suite, latest version, currently v2506) using POP3.  When I use that client and send one message to two recipients (one @live.com, the other @outlook.com) I instantly get two bounces, one for each recipient.  The details in the bounce say 'Dkim=fail'.

Having just installed Thunderbird 140.0.1 and set up a POP3 connection using the same settings as I use in Outlook 2016 and sent a message to the same two recipients I've NOT had any bounces and one of the recipients has confirmed they got the test message.  The other recipient will be at work so I don't expect to hear from them until it's convenient for them to reply.

[#8]

Excellent piece of sleuthing!

This raises the possibility of the issue being mail client related, even version of email client given my similar test did not encounter an issue.

When looking at the headers returned in the NDR attachments, is there anything there which hints at something relevant, which is not present in the successful delivery?

[#9]

@PhilipHeyes 

what for us consistently rejects with DKIM Failure via Plusnet works perfectly if sent via a 123Reg email a/c.

Is your 123reg account set to receive DMARC Aggregate reports (RUA) ?  If so can you check those from MS

I've certainly seen DKIM 'temperror' failures, for a domain hosted elsewhere, in DMARC aggregate reports from MS. For a domain thats seen by MS as low volume its not an issue as the mail is still accepted. For whats perceived by MS as a bulk sender it is a problem...

[#10]

I am afraid I am not the owner of the domain's 123Reg portal logon, merely a humble email user for this business.

[#11]

@Townman I have tried twice to reply to your post but both time my reply has disappeared.  I'm not trying again, sorry.

[#12]

Probably stuck in the spam filter ... one of the mods will unblock it shortly!

[#13]

In which case, they should only unblock my second attempt.

[#14]

Our distribution list is a MS Outlook Group.    A type of Contact list that typically has 6 or 7 emails in it.

The file that contains the X- entries is littered with personal information, it that what you are asking to see ?

If yes that is client data and I'd need to redact all the PI by hand.   But if you want it ... let me know.

[#15]

The error X headers should not have personal data therein.