Email Authentication for Outlook and Microsoft 365

Email Authentication for Outlook and Microsoft 365

Authenticating email for Outlook and Microsoft 365 means setting up SPF, DKIM, and DMARC for your domain so mail sent through Microsoft 365 is verified and reaches inboxes.

For Microsoft 365 senders

The same three records apply. Publish SPF including Microsoft's servers, enable DKIM in the Microsoft 365 Defender or admin portal and publish the CNAME records, and add DMARC. Microsoft runs its own reputation system, so authentication matters especially for Outlook and Hotmail delivery. See the microsoft blacklist check if you're blocked there.

The SMTP AUTH wrinkle

Separately from authentication records, Microsoft 365 disables SMTP AUTH by default on many tenants, which blocks application sending until an admin enables it. That's a sending-configuration issue rather than a DNS one, but it's a common Outlook-sending blocker.

How Nitrosend handles it

Nitrosend provisions the authentication records automatically, and placement is measured against seed mailboxes that include Outlook and Office 365, so Microsoft-specific problems surface in the data.

FAQ

How do I authenticate email for Outlook?

Set up SPF including Microsoft's servers, enable DKIM in the Microsoft 365 portal and publish the CNAME records, and add a DMARC record for your domain.

Why is my authenticated email still blocked by Outlook?

Microsoft runs a separate reputation system, and Microsoft 365 also disables SMTP AUTH by default, which blocks application sending until an admin enables it.