How would I know if an e-mail originates from Office 365?
I know I can look at the oldest Received header of a message to see where it originates from, but how would I use that header value to know it was sent from an Office 365 account?
It looks like the TLD exchangelabs.com is a candidate, but I'd like to know for sure.
I think it is outlook.com as first hop from server to your mailbox.
I think it is outlook.com
That's what I thought before looking into any e-mails. Did not find a single instance.
In Outlook you can configure the outgoing server(s) to be whatever you want (eg Google). There's absolutely no requirement to use outlook.com or any other particular server.
That I understand, I am not trying to determine whether it was sent with the Outlook application, but with Outlook/Office SMTP (server).
If it was sent with GMail then the first/oldest Received header would contain the TLD google.com or gmail.com (I checked).
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