Spam mail through SMTP and user spoofing

Posted by Josten Moore on Server Fault See other posts from Server Fault or by Josten Moore
Published on 2012-11-08T02:55:33Z Indexed on 2012/11/08 5:05 UTC
Read the original article Hit count: 232

Filed under:

email

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postfix

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smtp

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spam

I have noticed that it's possible to telnet into a mailserver that I own and send spoofed messages to other clients. This only works for the domain that the mail server is regarding; I cannot do it for other domains.

For example; lets say that I own example.com. If I telnet example.com 25 I can successfully send a message to another user without authentication:

HELO local
MAIL FROM: [email protected]
RCPT TO: [email protected]
DATA
SUBJECT: Whatever this is spam
Spam spam spam
.

I consider this a big problem; how do I secure this?

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