How can I prevent spam emails from using my address as the sender?

[Ivan Seeking]

Every once in awhile I get a spam email that shows me as the sender. At first I thought this may be a hacker issue and someone is using my computer, but no one I know gets spam from me, so I assume this is some sort of trick. Is it a trick, and if so, how do I block the sender?

 

[CFDFEAGURU]

This happened to me at work.

I have been sending myself some pretty good porn over the years. lol

The IT group stopped it but I don't know how they did it. I work for a huge company and a lot of other employees had the same thing happen to them. No one that any of us knew ever got an email from us, so I wouldn't worry about it unless it takes over your inbox.

I till check my local IT guy for you for a possible fix.

I checked with my IT guy and what has happened is that your email has been spoofed. Below is a link to a forum that might help. If not just search google for spoofing.

http://www.bluehostforum.com/showthread.php?t=132

Thanks
Matt

 

[Ivan Seeking]

Thanks, Matt.

 

[DavidSnider]

SMTP does not authenticate senders. You can say you are anybody.

 

[Ivan Seeking]

Sorry, I don't quite understand your meaning here.

 

[DavidSnider]

Sorry, I don't quite understand your meaning here.

S: 220 smtp.example.com ESMTP Postfix
C: HELO relay.example.org
S: 250 Hello relay.example.org, I am glad to meet you
C: MAIL FROM:<bob@example.org>
S: 250 Ok
C: RCPT TO:<alice@example.com>
S: 250 Ok
C: RCPT TO:<theboss@example.com>
S: 250 Ok
C: DATA
S: 354 End data with <CR><LF>.<CR><LF>
C: From: "Bob Example" <bob@example.org>
C: To: Alice Example <alice@example.com>
C: Cc: theboss@example.com
C: Date: Tue, 15 Jan 2008 16:02:43 -0500
C: Subject: Test message
C:
C: Hello Alice.
C: This is a test message with 5 header fields and 4 lines in the message body.
C: Your friend,
C: Bob
C: .
S: 250 Ok: queued as 12345
C: QUIT
S: 221 Bye
{The server closes the connection}

This is what an SMTP message (Email Request) looks like. I could put obama@whitehouse.gov in the MAIL FROM and send it to you.

 

[Ivan Seeking]

Okay, thanks, that definitely explains things. Given that I keep my antivirus, antispam, antispyware, etc, up to date, I didn't think the problem was on my end.

 

[mgb_phys]

As David described, you can put anything you want in the sender field.
Legitmate service providers will not normally let you send out mail which has a sender that doesn't match, but if you run your own mail server you can do anything.

The reason they used your address is that some mail server check that the sender address of an incoming message is valid, and block any spam with a fake address. Also some systems automatically let through any messages that have come from you, so setting the sender to the recipient has a higher chance of getting through.

The problem comes when they send it to someone else, we get complaints from people that we have spammed them, when a spammer has just used one of our addresses as a sender.