How do spammers send emails to your mailbox, that appear to be coming from your own address?

hi guys,

So a user at our work ended up getting an email, which appeared to be coming from themselves. So got an email from We use an Exchange server and are sitting behind Messagelabs.

I'm just curious how that happens? The other day, I did a telnet session from  my machine and sent an email 'from' my colleague to himself and he was curious as to how on earth that happens?

Are these two scenarios similar at all? I merely wanted to understand the concept and technicality behind it all.

Thanks for helping
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David SankovskySenior SysAdminCommented:
Hi Yashy,

the first thing I'd check is if your domain is whitelisted in Messagelabs - meaning every mail from your domain that's incoming into your domain will pass through regardless of the content.

The other thing is of course the SPF record for your domain.

If you could post the original headers of the mails, we might be able to assist you better,

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NerdsOfTechTechnology ScientistCommented:
It's fairly simple. The spammers will send out mail as YOU (to YOU too in this case) by "SPOOFING" your address and spewing out the email from their "NAIVE" stmp server (which doesn't require authentication).

Typically this is done overseas and is unstoppable by normal means.

Luckily for you you can FILTER out self-spam by excluding the "spam DOMAINS" you receive email from.

Such a SPF policy is needed to explain which hosts are allowed to send emails.

Without the ability to filter DOMAINS, SELF-SPAM continues to be a problem for many users.

One other tip: In some cases, the spoofer has acquired the password of the user by whatever means possible and is sending spoofed email through the victim's stmp server/account (authenticated); in this case, change the password!

Optionally, you may need to remove your domain from whitelists or even blacklist your domain in SPF (if you know non-authenticated email WON'T be sent). Get additional expert support if you need to execute this extra step.
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