Greylisting: Solution for Getting Rid of Spam Email - PowerPoint PPT Presentation

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Greylisting: Solution for Getting Rid of Spam Email


Greylisting is an effective as well as widely used technique for ensuring protection against spam emails. It is a method that makes sure that the users of email service remain protected against spam emails which never get delivered to them. – PowerPoint PPT presentation

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Title: Greylisting: Solution for Getting Rid of Spam Email

Greylisting Solution for Getting Rid of Spam Email
Table of Contents
  • Email
  • Web Server
  • Web Hosting
  • Greylisting
  • Email Delivery Process
  • How Greylisting Functions?
  • How Greylisting Functions (Continued)
  • Advantages of Greylisting
  • Challenges Encountered by Greylisting

  • Email (Electronic mail) refers to a message
    (mail) that gets transmitted and distributed
    electronically, via a network, among people that
    are using electronic devices.
  • It operates over the Internet. The current email
    systems function on a store-and-forward model.
    Messages are accepted, delivered, forwarded and
    stored by email servers. The electronic devices
    of the users of this service need to connect to a
    mail server or a webmail interface for the
    purpose of receiving and sending messages and for

Web Server
  • A web servers main function is to store, process
    and eventually deliver web contents and/or web
    resources to its clients. A web server refers to
    a server software or to a system that has one or
    more computers that run this software and which
    are able to satisfy client HTTP requests over the
    Internet and also over private LANs and WANs. It
    manages client HTTP requests with regard to web
    resources that are related to one or multiple of
    its configured/served websites.

Web Hosting
  • Web servers are provided in web hosting by web
    hosting service providers to their client website
    owners for the purpose of storing the files of
    their websites. Web hosting companies also
    provide the services and the technologies that
    aid in processing and delivering web contents and
    or web resources of their clients.
  • When these companies provide excellent service,
    these establish themselves as the Best Website
    Hosting Company or as the Best Windows Hosting
    Company or as the Top Cloud Hosting Company.


Greylisting defends email users against spam.
When greylisting is used by a mail transfer agent
(MTA), then any email that is from a sender that
isnt recognized by the MTA will be rejected
temporarily. In the event that the mail is licit,
the originating server will retry, post having
delayed it for some time. When enough time has
lapsed, this email will get accepted. Greylisting
is an effective measure that is used against mass
email tools that are used by spammers which dont
queue or retry mail delivery, as is normal with
regard to a legit mail transport agent. When
delivery is delayed, real-time blackhole lists
and other similar lists get the time that is
needed to identify as well as flag the spam
source. Hence, there is more likelihood of these
subsequent attempts detection as spam by other
mechanisms than there was prior to the delay that
had been caused by greylisting.
Email Delivery Process
The Simple Mail Transfer Protocol (SMTP) is used
for the purpose of transferring an email from a
sender to a recipient. An email that has been
sent over the internet will follow the path that
is described below. An email is composed by the
sender with his MUA (Mail User Agent). This can
be an email application that is locally installed
or a webmail interface. The Mail User Agent sends
the email by establishing an SMTP connection with
the Mail Transfer Agent (MTA) of the sender. This
is a software on the SMTP server which receives
and forwards mails. The email is forwarded by the
senders Mail Transfer Agent to the Mail Transfer
Agent of the recipient. If the email is accepted
by the agent, it gets delivered to the inbox of
the recipient. If the recipients local inbox is
synchronized by using the IMAP or POP3 protocol,
the email gets displayed as a new message.
How Greylisting Functions?
Greylisting occurs in the 3rd step of the email
delivery process. This is when the Mail Transfer
Agent of the recipient receives the email. The
receiving MTA requires the following data prior
to accepting an email. The sending mail servers
IP address The email address of the sender, via
the SMTP command MAIL FROM The email address of
the recipient, via the SMTP command RCPT TO The
above-mentioned data that is also referred to as
the envelope data is recorded in a list for
each incoming email, by the Mail Transfer Agent.
1-800-123 -8156
  • Whoa! Thats a big number, arent you proud?

How Greylisting Functions (Continued)
The Mail Transfer Agent will reject an email
initially, in the event that a set of envelope
data is encountered by it for the first time. An
error code is returned at this stage which
indicates that a technical problem has taken
place. The sending MTA is prompted to send that
particular email again after a specified waiting
period. This time when an attempt is made to
deliver the email again, the envelope data would
be present in the greylist and the email would
get delivered. A sending Mail Transfer Agent that
is not legitimate will usually not retry. As
there isnt any more attempt at delivering the
email, the spam email doesnt get delivered at
all. This is how the spam protection function of
greylisting works to get rid of spam emails and
the annoyance caused by such mails.
Advantages of Greylisting
  • There are many advantages of greylisting which
    are mentioned below, in no particular order.
  • It reduces spam substantially
  • It is turned on automatically (server wide)
  • It doesnt require any configuration by the user
  • The time delay involved in it, aids in
    blacklisting malicious senders
  • Time delays protect against new unidentified
  • It uses fewer resources when compared to most
    spam filters
  • It provides significant support to mail servers

Challenges Encountered by
The sending SMTP servers IP address must not
change. In the event that the senders SMTP
servers IP address changes, the incoming email
to the recipients SMTP server will be identified
as unknown. This will greylist the particular
email. Mail delivery might fail when the sending
mail server has been implemented or configured
incorrectly. If the senders Mail Transfer Agent
does not comply with the request to resend the
email, the mail wont be delivered. It can be
circumvented by spammers by using a significant
amount of resources. Spammers can send their
emails multiple times to bypass greylisting but
this requires a lot of logistical effort which is
not worth undertaking.
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