On 3/21/2024 5:48 AM, Gellner, Oliver via mailop wrote:
The topic about onmicrosoft.com has already been brought up multiple times on
this list, the last time in
January:https://list.mailop.org/private/mailop/2024-January/026871.html
ff
To sum it up: <customer>.onmicrosoft.com is the default domain for
everyone who uses Exchange Online. There are various scenarios why
legitimate emails can use this default domain, although most of them
come down to some misconfiguration or missing settings.
If all emails which you receive from those domains are spam then I
suggest you block it, as is true for every other domain. However a
general assessment that all emails which use onmicrosoft.com would be
spam is wrong.
A very good summary. We consider these provisioning domains not
suitable for real mail as a failure to follow standard postmaster
hygiene such as using IPs with rptrs. The KAM Ruleset includes a rule
called KAM_ONMICROSOFT that has a score of 5.0. Not quite a poison pill
but very close.
Regards,
KAM
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