If you haven't already sorted out your SPF, DKIM, DMARC it may be time to do it

[Kitkatninja]

Came across this blog today:

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Starting 5 May 2025, Microsoft Outlook is implementing stricter email authentication requirements for high-volume senders (those sending over 5,000 emails per day). This change is part of Microsoft's ongoing efforts to strengthen the email ecosystem and protect users from spam, phishing, and spoofing attempts.

If you're receiving a "550; 5.7.15 Access denied, sending domain [SendingDomain] does not meet the required authentication level" error when sending emails to Outlook.com addresses (including hotmail.com, live.com, and outlook.com domains), your domain and sending service doesn't meet the new authentication requirements.

 

 

While 5000 emails per day may sound alot, it only takes a large secondary school to send out 2-3 emails to every student regarding exams (or similar similar to hit that number).

[TwistedHelixis]

Google implemented something like this last year.

 

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Starting February 2024, Gmail requires the following for senders who send 5,000 or more messages a day .... blar blar

 

Recently setup DMARC on all my primary schools, not because of this issue, but because its a good thing to do anyway.

Edited April 30, 2025 by TwistedHelixis

[paulkerton]

Absolutely worth setting up, we're already basically denying any emails incoming that isn't set up. Especially with DKIM

[DalekSec]

This is email server hosting 101, all 3 should be setup as default! 

[drutt]

For those who have not got around to doing this yet, I found this guidance useful back when I implemented it:

 

https://www.ncsc.gov.uk/collection/email-security-and-anti-spoofing

Edited April 30, 2025 by cnewstead

[TechMonkey]

Ok, apologies in advance for being blunt but, "If you haven't already sorted out your SPF, DKIM, DMARC" why the heck not?

[andy_b]

I'd add MTA-STS to that list too.

[k-strider]

when setting this all up (if you haven't) at the same time as setting this up register with https://www.ncsc.gov.uk/section/active-cyber-defence/sign-in-register

as their mail check service is really useful to make sure everything is in place and working correctly shame they are depreciating their dmarc reporting.