[AusNOG] Microsoft 365 - Junk Policy (last 2 weeks)

[David Rawling]

Hi Luke

I can confirm that we've been seeing quite a lot of this across a
number of Office 365 tenants; both our own and several we manage (I'll
note that I am subscribed to AusNOG from my personal account not the
affected tenant).

As we're one of the affected tenants, we've been able to dig quite
deeply into the behaviour - in our case, it seems to be that almost all
"new" messages in a thread are successfully delivered to us, but once
it becomes a reply-fest it gets junked. There's some thought that it
could be related to one or more links in our signature - not that it's
a particularly large or "spammy" signature, though. No SPF, DMARC or
DKIM failures here. No obvious reasons it would be marked junk - the
SCL is below our threshold, etc.

What's frustrating is that so far, it's only affecting some people in
our tenant. I've not had the problem with messages I send and receive,
but there are others where it's 90% failure. I do have a different
signature file - very different formatting though it looks the same to
the recipient. I was thinking that might be related, but no dice so
far.

So you're not alone but we have absolutely no idea what's breaking.

Dave.
-- 
David Rawling - Principal Consultant
PD Consulting and Security

t: +61 41 213 5513  |  e: djr at pdconsec.net

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On Fri, 2023-03-31 at 16:55 +1100, Luke Thompson wrote:
> Hi all,
> 
> Strange question though curious if anyone's seen the same.
> 
> We've had a range of clients reporting very intense junking behaviour
> with M365, whether sending or receiving, if there's a M365 tenant 
> involved it seems to be hitting Junk for reasons that aren't clear.
> This 
> is with SPF/DKIM/DMARC/etc all passing.
> 
> I'm wondering if potentially a new policy has shipped which is 
> over-reaching somewhat, as no bounce-backs are being received so it's
> a 
> case of delivered-but-not. This is across a range of clients and 
> clients' clients.
> 
> If we'd only heard of this from a single client we'd not think much
> of 
> it, though this is both ways and across a range of tenants. Would be 
> good to know if there's any substance to it.
> 
> As we don't run M365 nor have responsibility for impacted tenants,
> the 
> request here is to check with the IT community. Thank you.
> 
> Cheers,
> Luke
> 
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> AusNOG at lists.ausnog.net
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