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The X-Originating-IP (not to be confused with X-Forwarded-For) email header field is a de facto standard for identifying the originating IP address of a client connecting to a mail service's HTTP frontend. When clients connect directly to a mail server, its address is already known to the server, but web frontends act as a proxy which internally connect to the mail server. This header can therefore serve to identify the original sender address despite the frontend.


The general format of the field is:

X-Originating-IP: []


In 1999 Hotmail included an X-Originating-IP email header field that shows the IP address of the sender.[1][2] As of December 2012, Hotmail removed this header field, replacing it with X-EIP (meaning encoded IP) with the stated goal of protecting users' privacy.[3]

See also[edit]


  1. ^ "Q&A: Fighting Spam at MSN Hotmail". Microsoft.com. 1999-09-22. Retrieved 2012-05-28.
  2. ^ Declan McCullagh (2001-06-16). "The Wrong Way to Do Dirty Tricks". Wired.com. Retrieved 2012-05-28.
  3. ^ what does X-EIP mean in an email message source