DMARC for Microsoft 365, How to Stop Email Spoofing and Protect Your Brand
Email is still the number one channel for phishing, invoice fraud, and business email compromise. One of the most damaging tactics is spoofing, when attackers send emails that appear to come from your domain.
For law firms, healthcare practices, financial firms, and professional services in Phoenix, spoofing is more than annoying. It can harm client trust, trigger compliance concerns, and lead to wire fraud.
That is why DMARC matters.
This guide explains DMARC in plain English, what it does, how it works with Microsoft 365, and how to roll it out safely without breaking legitimate email.
What is DMARC?
DMARC stands for Domain based Message Authentication, Reporting, and Conformance. It is an email security standard that helps mailbox providers decide whether an email claiming to be from your domain should be trusted.
DMARC builds on two other standards:
SPF checks whether the sending server is allowed to send mail for your domain.
DKIM adds a digital signature that proves the email content was not altered and that it came from an authorised system.
DMARC adds enforcement. It tells providers what to do if SPF or DKIM checks fail, and it gives you reporting so you can see who is sending email on your behalf.
Why DMARC matters for businesses
Without DMARC enforcement, attackers can often spoof your domain and send phishing emails that look legitimate to recipients.
DMARC helps you:
Reduce spoofed emails that pretend to be your firm
Protect clients, vendors, and staff from impersonation scams
Improve email deliverability for legitimate messages
Support compliance expectations and cyber insurance questionnaires
Get visibility into unknown systems sending mail for your domain
For many organisations, DMARC is one of the highest ROI security improvements because it reduces a common, high impact attack path.
Common examples of spoofing that DMARC helps stop
“Invoice updated, use new bank details” emails
“Urgent request from partner, send gift cards” scams
Fake password reset messages pretending to be IT
Phishing emails that use your company name and domain to look real
Impersonation of HR for payroll changes or W-2 requests
Even if your internal users are trained, your clients and vendors can still be targeted using your brand.
DMARC policies, what do none, quarantine, and reject mean?
DMARC uses a policy that tells receiving mail servers what to do when an email fails authentication.
p=none
Monitoring only. Email is delivered as usual, but you get reports. This is the safest starting point.
p=quarantine
Suspicious mail should be treated as risky, often sent to spam or junk. This is a middle step.
p=reject
Unauthenticated mail claiming your domain should be rejected. This offers the strongest protection against spoofing.
A safe rollout usually moves from none, to quarantine, to reject once you confirm all legitimate senders are properly configured.
The biggest mistake with DMARC rollouts
The most common issue is turning on strict enforcement before confirming every system that sends email using your domain.
Many businesses use third party tools that send email as them, such as:
CRM and marketing platforms
invoicing or payment systems
ticketing systems
website form tools
document signing platforms
HR platforms and applicant tracking
printers and scan to email devices
DMARC reporting helps you find these senders, so you can configure them correctly before enforcing quarantine or reject.
How to roll out DMARC safely
Here is a practical approach that works well for small and mid sized Phoenix businesses.
1) Start with visibility
Begin with a monitoring policy so you can see what is sending email for your domain.
What you are looking for:
authorised platforms that need configuration
unknown senders that could be abuse
systems that fail DKIM or SPF checks
2) Fix legitimate senders
For each legitimate platform, ensure it sends email in a way that passes SPF or DKIM alignment for your domain.
The goal is simple:
legitimate senders authenticate correctly
spoofed senders fail and get blocked later
3) Move to quarantine
Once reports look clean, move to quarantine for broader protection while still allowing a safety net.
4) Move to reject for strong protection
When you are confident legitimate mail passes authentication, reject provides the best defence against spoofing.
How DMARC supports Microsoft 365 security
DMARC does not replace tools like MFA, Conditional Access, or endpoint protection. It complements them.
A strong Microsoft 365 security baseline often includes:
MFA enforced for all users
Conditional Access to block risky sign ins
mailbox auditing and alerting
phishing protection and safe links
DMARC, SPF, and DKIM for domain protection
Together, these controls reduce account takeover and impersonation risk significantly.
Quick checklist, is your domain protected?
Use this as a simple DMARC readiness check:
SPF is configured and not overly permissive
DKIM is enabled for Microsoft 365 and key platforms
DMARC policy exists, even if it is monitoring only
You review DMARC reports regularly
You have a plan to move toward quarantine or reject
Third party senders are documented and controlled
