Be Alert: The SMTP Security Threats in the Nutshell

The Internet users experience SMTP security threats everyday through millions of junk emails, containing malicious attachments, phishing attempts, and tasteless contents. The origin of such emails is mostly from botnets, a fleet of computers, smartphones and IoT (Internet-of-Things) devices taken over by malware with the goal of stealing their CPU cycles for the virus author‘s purposes. The owners of those zombie devices have no idea that their devices are no longer in their full control, but part of a huge conspiracy to sending spam emails and launch DDoS attacks. People are often Googling for the question: How to permanently stop spam emails? It is a question that even Google has no exact answer, given the number of hits it provides in its own results page:

SMTP is used as the common mechanism for transporting email among different hosts within the transmission control protocol/Internet protocol (TCP/IP) suite. It is an application layer protocol. Under SMTP, a client SMTP process opens a TCP connection to a server SMTP process on a remote host and attempts to send mail across the connection. The latter is being deprecated in favor of the former, with the rise in popularity of webmail services like Gmail, and the old but still reliable Yahoomail. An SMTP-based process can transfer electronic mail to another process on the same network or to another network via a relay or gateway process accessible to both networks. An e-mail message may pass through a number of intermediate relay or gateway hosts on its path from a sender to a recipient.

SMTP Security Threats

Many ISPs restrict access to their outgoing mail servers to provide better service to their customers and prevent spam from being sent through their mail servers, but SMTP security threats still exist. There are several methods for establishing restrictions that could result in denying users‘ access to their outgoing mail server, a counterproductive security arrangement. Bulk mailers have taken advantage of SMTP security threats to send huge volumes of mail with bogus return addresses. This result in slowing down servers due to delays caused by SMTP security threats, causing legitimate emails being irrelevant the moment it reaches its intended recipients.

To fix that specific problem caused by SMTP security threats, the origin of a spam email should be identified. An e-mail message typically transports through a set of SMTP servers before reaching the destination host. Along with this ticket, messages get approved by the intermediate SMTP servers. The stamps release tracking information that can be identified in the mail headers. Mismatches between the IP addresses and the domain names in the header could unveil the real source of spam mail. The real domain names that correspond to the indicated IP addresses can be found out by executing a reverse DNS lookup. Most recent versions of email clients like Outlook and Thunderbird have already incorporated this functionality, which generates a Received: header line that includes the identity of the attacker. If we analyze it carefully, it is an elegant workaround to the SMTP security threats, as cyber criminals continue to find exploits as we speak.

The basic SMTP protocol used by a mail server to send, receive, or route e-mail across a network requires the sender‘s address and the recipient‘s address to be specified. Normally, either the sender or the recipient address is in the server‘s domain. Some SMTP servers accept any sender or recipient address without checking whether at least one of them is in the server‘s domain, one of the long time documented SMTP security threats. On such servers, it is possible to supply a fake sender address by exploiting SMTP security threats and an arbitrary recipient address, which greatly facilitates the spread of spam through an SMTP security threats. Even SMTP servers, which generally do not allow relaying, do allow it if the session originates from a host in the server‘s domain or from a host from which relaying is explicitly permitted. With this it seems the SMTP security threats, this specific “bug” is by design. If the scan is performed from such a host, a false alarm may result. Microsoft Exchange and Unix‘s Sendmail platforms already addressed this issue with an available patch against SMTP security threats.

By denying access to a sending machine with a firewall, many companies and ISPs have been blocking the receipt of unwanted mail from known sources. The “blocked” senders of junk mail may attempt to deliver it through another computer by requesting the computer to route that mail for them. Senders of unsolicited e-mail can also use SMTP security threats to hide their real identity by manipulating the headers in the message and then sending the message through the client‘s system for delivery to its final destination. This SMTP security threats, this time through “spoofing” action gives the appearance that the message originated from the relaying server.


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