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

[#1]

For the next suitable communication we are going to try in HTML as usual but
with an Unsubscribe link in bottom of the Signature

Unsubscribe as  mailto:<our.name>@<account>.plus.com?subject=Unsubscribe

I see this mentioned as a requirement in the recent link to the Microsoft's email acceptance criteria,
we shall keep it simple and write back to the sender so if the email is parsed it is valid.

Plain Text

HTML works perfectly via gmail.com and 123Reg, we already know the format is just fine for Microsoft
in single destination and multi destination messages.

[#2]

@Townman

My simple testing today has been as follows:

1) using POP3 Outlook 2016, send one message TO [someone]@live.com, [someoneElse]@outlook.com

The subject was plain text, the body was plain text, only regular letters from the English alphabet, plus some full stops and commas.

In the recent past such a message would instantly trigger at least one, more often, two bounces (Dkim=fail).  This time though I got no bounces and I know for sure that the message to [someElse]@outlook.com reached the recipients Inbox almost instantly.

The difference between this test and recent test sends was that this message was explicitly formatted as 'plain text'.

2) using POP3 Outlook 2016, send one message TO [someone]@live.com, [someoneElse]@outlook.com

The subject was plain text, the body was plain text, only regular letters from the English alphabet, plus some full stops and commas.

Again, no bounces and I know for sure the message to [someElse]@outlook.com reached the recipients Inbox almost instantly.

The difference between this test and test 1) was that this message was explicitly formatted as 'rich text'.

3) using POP3 Outlook 2016, send one message TO [someone]@live.com, [someoneElse]@outlook.com

The subject was plain text, the body was plain text, only regular letters from the English alphabet, plus some full stops and commas AND one word formatted in bold.

Again, no bounces BUT this message seems to have disappeared, I know for sure it did not reach [someElse]@outlook.com's Inbox or their Junk folder.

The difference between this test 3) and test 2) was only the inclusion of a word formatted in bold, i.e. test 3) was also explicitly formatted as 'rich text'.

I've yet to hear back from [someone]@live.com so I don't know if that recipient's experience has been the same as that of [someone]@outlook.com, but I will let you know as soon as I hear.  Meanwhile, does any of this help?

[#3]

@Townman 

The experience of [someone]@live.com was the same as that of [someElse]@outlook.com.  They got both messages I sent as test 1) and test 2), but the third one is completely missing, I've still not had any bounces from it but it's not reached either of the recipients.

I've also just tried a fourth test, to check out @PhilipHeyes's idea of sending as HTML but adding an unsubscribe link to a signature.  Doing that produced just one bounce, which came from the copy to [someoneElse]@outlook.com, i.e the second address I put in the TO field.  The error is the usual 'Dkim=fail'.

[#4]

My workaround is to send emails to MS-related addresses via webmail which I think go as plain text. Could this be the reason why I get no failures?

[#5]

That’s an interesting theory, one I cannot explore myself until Tuesday.

[#6]

Um. Horses go 'neigh' (rhymes with 'nay'). The impossibility parameter could be 'nigh'.

Embedded weblinks in mails to MS mail recipients? And MS then 'reworking' those weblinks (possibly to protect at least some subscribers of their mail services from being hit with scammy stuff?)

I've seen some extended delays of mail delivery to (at least) one MS e-mail address - with the original URL in the e-mail being rewritten in the received e-mail. This occured /before/ these problems reported here.

Therefore I also have to posit that MS may have been working on 'stuff' before the problems arrived at the doors of Plusnet customers. The moving goal posts could have started some time back.

Could be related. Or could not be related. Insufficient data.

[#7]

I thought I'd mention here, in case it is related to any reconfiguration work underway by Plusnet......

This morning I cannot send e-mails to any destination, either via Outlook 365 or Plusnet webmail.

In webmail I am getting SMTP Error (451): Authentication failed.

In Outlook 365 I get the attached.

[#8]

Yep,, looks like the SMTP  server has thrown another wobbly.

@Townman  / @MisterW  ?

[#9]

It seems to be the incoming server , my email client is reporting login failed using the primary account. I've escalated it... 

[#10]

@MisterW Cheers. Like @ebforum , I can't send, but MailWasher seems to be happy - no error reports on there.

[#11]

Both servers, I think, @MisterW - I can't send - just get stuck on 'sending', and a message I sent from one of my iCloud accounts to my main PN one has not arrived. Strangely, MW  doesn't say it can't find the server, just doesn't pick anything up.

[#12]

@jab1 yes, you're right  it does seem to be the outgoing server, its just the mail client reporting the error badly.

I tried the email diagnostics and the imap server seems ok, but the smtp one fails!

[#13]

Just waking up - got problems here too - will get to look at things after a coffee.

[#14]

Probably unrelated, but I can receive - from most of my regular news/promotional contacts, but test messages from my iCloud and Yahoo accounts are not getting through.

[#15]

Issue seen briefly at 8pm now appears to have been resolved.  Discussions continue.