want to understand emails delivery from MTAs (sendmail)

Posted on 2008-10-26
Last Modified: 2010-04-18
A quick question regarding MTAs and especially for sendmail.

When we send an email from any MTA (e.g. sendmail) the recipient MTAs check the sender mail server or the email From adddress (e.g. in their spam filters? I mean how they verify that this email is not a spam?

Question by:samengr
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Expert Comment

ID: 22807367
There are many tests to identify spam, beginning at the inbound connection where the IP address can be compared against known spammers (this is sometimes done at the firewall). The SMTP HELO sequence can then be used to check for spam sources. generally, if it has made it this far, the SMTP server will accept the message.

The next step is to parse the message header, and one of the tests, as you've suggested, is to check the from address against a list of known spammers. The lists can be global or per-user, and include known spammers (blacklists) and good addresses (whitelists) that should never be flagged as spam.

But because these values are easily forged, anti-spam software incorporates a long list of tests to identify spam. Have a look at the documentation for SpamAssassin to see a good description of the tests.

The end result is often not a spam/not-spam answer, but a rating, sort of 1-10, and the user sets a threshold.
LVL 32

Accepted Solution

Kamran Arshad earned 125 total points
ID: 22820303

Also read the SMTP RFC for comprehensive information on the working on protocol;

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