Here are the resulting email headers, grossly simplified for this example: Received from His email software always sends email via the MTA host named “.” Alice always retrieves her email from the host “.” Bob’s email follows this path: Bob’s client carries the name “” in the mail system. A Sample Traceīob sends an email to Alice. The host address is usually in domain name format, though the IP address may also be provided, usually in square brackets as shown in the “from” clause. The host addresses are highlighted in red. Here are the relevant clauses from the above example: from Įach of these clauses contains a host address and possibly other information in parentheses. Ignore the “with” and “for” clauses, or any others. For email tracing, we care about the “from” clause and the “by” clause. The Received header contains several clauses, usually started with a preposition. ![]() We ignore the ones that start with “X-” or end with “-SPF” or just embed the word “Received” somewhere in the middle. ( )ĮCDHE-RSA-AES128-GCM-SHA256 (128/128 bits))Īs email has evolved, a lot of headers have appeared, many of whose names contain the word “Received.” For this exercise, we only pay attention to “Received:” headers. Here is a typical Received header: Received: from The recipient can see the email’s whole path by tracing the Received headers back to the sender. While there’s no way to prove they were legitimate, the headers I reviewed looked believable.Įach time an MTA processes an email message it adds a header (the “Received:” header) to the front of the email message. I used the following technique to assess whether the #PodestaEmails leaked during the 2016 presidential elections were “ obvious fakes,” as claimed by one observer. These servers are generally called mail transfer agents (MTAs) and they use the Simple Mail Transfer Protocol (SMTP). When we send an email, we connect to a server to deliver it for us. If the final Received header didn’t come from my bank, then I know it’s fake. I use this technique more-or-less daily to look at potential phishing emails. ![]() We can increase our confidence in an email a little, though, by tracing its path through the mail system. Until every email client includes encryption and reliable authentication, we should always doubt an email’s source. ![]() There is no way to verify an email’s contents except through cryptography.
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