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Spoofed Email

Posted on 2016-09-21
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Last Modified: 2016-09-22
One of our users on Exchange Server has been receiving messages from our system with the subject "Undeliverable..." from "Mail System Delivery".  We've determined that the one user's email address has been spoofed from a server in Mexico.  In the past 2 hours, she has received maybe 10 of these messages.  Is there a way to "unspoof" the user's email address?
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Question by:rsaba
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ScottCha earned 250 total points
ID: 41809647
No, spoofing is done on the outside and there is little if anything that can be done to stop it.

About all you can do is change you user's email address and block the old one using a transport rule.
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by:John Hurst
John Hurst earned 250 total points
ID: 41809653
Or (as I have used successfully) change the user's password. The spoofing will die down and they cannot get back in. Changing email address is certainly good but people do not like doing that. Changing passwords is second best and takes time.
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by:Dave Baldwin
ID: 41809654
Scott is correct.  This is a common way for spammers to get past the spam filters because nobody blocks email sent to themselves.
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by:El Fierro
ID: 41809659
i had that recently happen, i ended up resetting the users account password. after i did that the spoofed undeliverable emails stopped. i also rans some antivirus/malware scans on his machine. he was the only one with that problem. it stopped but its on my to do list to further investigate.
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by:rindi
ID: 41809714
I can't imagine how changing a password would stop email spoofing. You don't need the user's password to spoof him. You'd only need it if you used his actual mail server and account to send email. But that isn't spoofing.
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by:John Hurst
ID: 41809716
If the account requires authentication, the spoofer will be trying (may be trying) to send from a changed account.
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by:rindi
ID: 41809736
He doesn't need the account at all. For spoofing emails he uses another mail server (probably with open relay), and he can spoof your real mail account so it looks the same. If the message he sends doesn't reach the recipient (because he doesn't exist, spammers try every possible email combination, and a large number of them won't exist), it bounces back to your account (and not the spoofing account). with the message that it failed. For that he doesn't need any knowledge of your actual account, he may just have guessed a name@domain.x combination and happened to find one that actually exists.
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by:Todd Nelson
ID: 41809740
Do you have a SPF (TXT) record configured in your public DNS for your email domain?

It will help a bit provided the recipient domains are checking for valid sender origins--which a spoofer generally does not send from within your environment.

An example of an SPF record would look similar to this...

v=spf1 mx a ip4:ENTER_YOUR_OUTBOUND_IP_ADDRESS_HERE -all

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References...
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by:John Hurst
ID: 41809744
I know there are several ways to spoof email and yes some of them do not use an account.
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by:jhyiesla
ID: 41810739
It's a long term solution, but yo could invest in an anti-spam service that includes an anti-spoofing feature. We use MimeCast and it works really well.
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