Email headers is still your best friend. Emails from hotmail aol yahoo google cant really have forged headers because the email you write through that SMTP has to go through their server and to forge headers like that would require changing settings in the mail server. If its an email from a domain server which the sender can control and change settings, it is possible to mask IPs etc but your email server should generally deny those types of emails. Hotmail, google, yahoo mail generally won't give information location-wise as where the email sender is unless its a criminally evident email that is being investigated by a law enforcement agency, but they should be able to.
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