Why does Office 365 hosted exchange use 25.x.x.x IP addresses?


EQ Forum Admin
Staff member
It was recently reported that users of the Office 365 exchange service are seeing 25.x.x.x IP addresses in their full email headers.

As far as I can tell, these addresses may be used "internally" by Microsoft, but are not used for relaying email to other service providers.

I came to that conclusion because the IP addresses I checked from the full headers of emails do not have a sender score, for example:

Lookup for - SenderScore.org

The lack of PTR records or mention of Microsoft in a whois lookup is interesting:

OrgName: RIPE Network Coordination Centre
Address: P.O. Box 10096
City: Amsterdam
PostalCode: 1001EB
Country: NL
Updated: 2013-07-29

Update: A Microsoft rep commented that this address range is used for Microsoft Exchange Online Protection (EOP) service.