According to the SMTP protocol, several SMTP commands can be placed in one network packet and “pipelined”. For example, whenever an email with a CC: header is sent several SMTP “RCPT TO:” commands may be placed in a single packet instead of one packet per command. The SMTP protocol actually requires that errors are checked… Read More »
According to the RFC 5321 section 4.1.4 “An SMTP server CAN verify that the domain name argument in the EHLO command actually is same as the IP address of the client and if it fails, the server SHOULDN’T refuse to accept messages on that basis”.Hence to be in compliance with the RFCs, rejecting connections must… Read More »
Greylisting (or graylisting) is a technique of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will “temporarily reject” any email from a sender it does not recognize as a legitimate one. If the mail is legitimate, the originating server will, shortly stop for some time and tries again and if sufficient… Read More »
An SMTP server has introduced a deliberate pause before sending the greeting banner to the client. In client server architecture, the client is required to wait and it is not supposed to send the message to the server unless it receives the banner. However, many spam-sending machines begin to send out messages before the banner… Read More »
Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks. SMTP was first defined in RFC 821 (STD 15), and last updated by RFC 5321 (2008) which includes the extended SMTP (ESMTP) additions, and is the protocol in widespread use today. Enforcing the requirements of the… Read More »
Some of the people advocate responding aggressively to spam; in other words, that means, “spamming the spammer”. The underlying reason is to make spamming less attractive to the spammer by increasing the spammer’s overhead. There are several ways to reach the spammer but then they may even lead to retaliations by the spammer. There is… Read More »