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Spam analysis IN the SMTP protocol
by Stephane
The benefits of analysis during SMTP communication
On the Internet, e-mail messages are exchanged using the standardized SMTP protocol. Data (mail) communication in this protocol is organized by the following syntactic sequence: HELO or EHLO, MAIL FROM, RCPT TO, DATA. After each command, the destination server responds to the sender by accepting (code 200) or rejecting (code 500) the command.
Currently, most anti-spam solutions accept e-mail and process it after the fact, whereas analyzing it directly during SMTP communication offers many advantages. Email filtering in the SMTP transaction enables an immediate response to the remote server if the email is accepted or rejected. In the case of a refusal, this is not a rejection of the e-mail (carried out after an acceptance) but a refusal of acceptance by the SMTP server. This offers two advantages:
– As the mail is directly refused by the contacted server, the sending server is informed of this processing. It can therefore bounce back to inform the sender of the message that it has been refused. This is useful in the case of false positives, where the anti-spam solution considers an e-mail as spam when it isn’t. In this case, the sender will be notified that the email has not been received. In addition, using a URL passed to the sender via the refusal message, the latter is redirected to an authentication page to enable him to release his email himself. As soon as a control code (Turing test) is entered, the e-mail is returned to the recipient and the sender is automatically whitelisted.
– In the same way, servers that send spam are informed when an e-mail is refused. However, most of them operate a system for deleting invalid e-mail addresses, so as to lighten their workload next time. In this way, the email address will be considered non-existent by the system and gradually removed from spammers’ lists.
Today, this type of solution guarantees your system’s protection against spam without risking damage to your business. This type of technique proposed by Oktey is implemented in the Altospam outsourced antispam solution.
