Not sure if I'd call it extreme, but a marked increase beginning Feb 6th.  

Alex Brotman
Sr. Engineer, Anti-Abuse

-----Original Message-----
From: mailop [] On Behalf Of Dan Malm
Sent: Friday, February 09, 2018 3:57 AM
Subject: [mailop] Extreme amounts of SMTP auth from microsoft/outlook IPs


I'm seeing an extreme amount of SMTP authentications (over 600/s) from the 
microsoft owned range on my customer SMTP servers.
It's just auth, with valid credentials, and then it disconnects right after so 
no attempts to send any mails have been done for the vast majority of these 
connections. A small amount of valid mails are being sent from this range 
though. HELO indicates it's from So seems like their system for 
sending with your own domain through external servers has gone a bit haywire...

I've sent a mail about it, but I'm a bit curious if anyone 
else is seeing the same?

BR/Mvh. Dan Malm, Systems Engineer,

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