Email notifications from this Forum not arriving in Outlook

[#1]

The subject covers it.
I have recently started to use Outlook for Android to fetch PlusNet mail via IMAP.
Concurrently using Gmail for Android to fetch the same email.
Notification emails from this Forum only arrive in the Gmail client, i.e. Microsoft must be rejecting them. They are not diverted to Spam, that Outlook calls Junk.

[#2]

IMAP is a view of the current contents of the mailbox.

Is the Gmail client configured for POP3 and is collecting & then deleting emails from the mailbox ?

[#3]

Both Outlook and Gmail are configured for IMAP, i.e. both leave messages on the server.
The issue is Outlook does not display forum messages, but if I look in Gmail they are there.
Outlook must be rejecting those, I suspect a DKIM signing or suchlike is misconfigured.

[#4]

DKIM / SPF / DMARC have already been processed if the mails are in the mailbox.


Is Outlook doing something unexpected with the display of messages ?

I recall my initial issues with Outlook APP making new messages hard to spot if it clustered emails into a conversation
as opposed to displaying all new messages as an individual entries.

Perhaps Turn Organize By Conversation Off/On to see if it helps.

[#5]

I have focussed inbox OFF, group by conversation NO.
I get that DKIM / SPF / DMARC must have passed to get in the mailbox, but it seems that Microsoft is rejecting something in the headers that Google allows.
I guess I'll have to ask an AI what it thinks.

[#6]

A suggestion might be to reset & re-import all the messages from the mail box,
I believe there is usually an option to do this in MS Outlook.

[#7]

Email from noreply@community-mailer.plus.net appear to be rejected because:
"Cannot forward emails that are not authenticated".