How does Perfectmail reject spam?
Posted by Andrew Weisz on 13 July 2012 04:33 PM
PerfectMail will always send a Rejection Notification for e-mail addresses that it cannot validate or messages that cannot be delivered to the destination mail server. However, these messages are not Non Delivery Reports (NDRs), nor are they Backscatter. PerfectMail sends "SMTP Rejection Notices".
There are two types of rejection messages that can be created in e-mail: SMTP Rejection Notices and Non Delivery Reports (NDRs).
SMTP Rejection Notices:
PerfectMail uses SMTP Rejection Notices. These rejection notices are exchanged during the SMTP mail exchange; when e-mail is being exchanged between mail servers. PerfectMail is able to give notification during the e-mail exchange because it is a Live Filtering Solution. PerfectMail analyzes, filters and responds to e-mail in real time, during the message exchange. This guarantees that PerfectMail sends a rejection notification and that the sending server received it; which is implicitly the correct server to send the notification to. By definition, such messages are not Backscatter.
Unfortunately, PerfectMail cannot control what a remote mail server does with such messages. Most mail servers will delivery the SMTP Rejection Message to the original sender; however some mail servers may discard such notifications.
Non Delivery Reports (NDRs):
Non Delivery Reports (NDRs) (also known as "bounce" messages) are automated rejection messages created by some mail servers to the "apparent" sender of an e-mail. Such messages are generally created after an e-mail message has been transmitted to the recipient server. Analysis of the incoming message, including anti-spam decisions, routing decisions deliverabilty is determined after the message has been accepted. If there is a delivery problem a separate e-mail, the Non Delivery Report, is generated and sent to the apparent sender of the original e-mail.
NDRs are susceptable to Backscatter issues (see below). After the message is received the mail server has no ability to validate the original sender of the e-mail message. Spam messages often are sent with forged sender addresses (often legitimate e-mail addresses, but not of the sender), which will receive these unexpected NDRs.
PerfectMail analyzes, filters and responds to e-mail in real time, during the message exchange. This eliminates the need for NDRs and alows the use of SMTP Rejection Notices in real-time.
Backscatter is incorrect automated rejection (or bounce) messages sent by mail servers, usually resulting from incoming spam. Such messages are viewed by the recipients as a form of spam, since the recipient is (by definition) not the originator of the e-mail being rejected.
Backscatter usually occurs because worms and spam messages forge their sender address (often with legitimate e-mail addresses). Mail servers configured to send Non Delivery Reports (NDRs) will incorrectly bounce the message back to the forged sender address.
Mail servers that generate email backscatter can end up being listed on various DNS Black Lists, and be in violation of the Terms of Service of some Internet Server Providers.