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Outlook for Windows Gets External Mail Tagging

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External tagging for Exchange Online messages first appeared in March 2021 with general availability in October 2021. This only covered OWA, Outlook Mobile, and Outlook for Mac. From November 2022 the Desktop Outlook client received external tagging.

As you’d expect, external tagging works exactly the same way as in other Outlook clients. Any email received from an external domain is tagged as external. External email warning helps to alert users from clicking malicious links, phishing emails sent by external senders. It plays a vital role in protecting against spam and phishing threats

Raising User Awareness

To be fair, that’s the point. The idea of external tagging is to highlight these messages to users with the hope that people will pay extra attention to any links and other content. Organizations have used transport rules to stamp inbound email with similar labels for years and highlighting email does help.

External tagging also helps to avoid recipients falling into the trap of business email compromise (BEC). Many BEC attacks happen due to compromised accounts.

One is when email appears to come from an internal domain but really comes from a domain with a very similar name that’s set up by attackers with the aim of duping recipients. Humans might be fooled when an attacker swaps 1 for an l in a domain name, but a computer won’t be.

Outlook Desktop view of external sender: 

Outlook on the web view of external sender: 

External email warning

Outlook for iOS view of external sender: 

enable External email tag


Enable External Email Warning Tag in Exchange Online (
Outlook for Windows Gets External Tagging At Last (

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