Anti-spam technology - the first generation
It's difficult to sharply distinguish between pre-existing features available in most MTAs and first-generation anti-spam features because pre-existing features were used to combat spam together with new features developed largely to address the spam problem. For example, message header and envelope tests as well as simple DNS tests were motivated primarily by the need to combat spam but cannot directly distinguish between spam messages and other messages.

Basic MTA controls
MTA controls that restrict communications based on networks and domain names, e.g., to prevent "relaying" are not an anti-spam technology. Some of these features predate the spam problem and exist primarily for the purposes of security.

White lists and black lists
White lists and black lists in an MTA are a logical extension of basic MTA controls used primarily as a crude (and ultimately ineffective) tool to control spam. Although white lists and black lists are an important anti-spam feature, they are not a new technology because they merely extend rather than depart from historical MTA controls. MTAs in email anti-virus and security/compliance products had this feature before it was characterized as an anti-spam capability.

Simple keyword searching
One of the first methods used to combat spam was simple keyword searching. This functionality existed prior to spam becoming a major problem on the Internet, as a part of content filtering and compliance solutions and server-based email anti-virus products.

This approach can be used to identify a subset of spam messages, but is not effective because it fails to recognize word variations or context and can results in many false positives (legitimate email misidentified as spam).

MTAs in email anti-virus and security/compliance products had this feature prior to its use as an anti-spam tool. Simple keyword searching is trivial for spammers to defeat through simple variations in spelling or alternate word choices.

Message header and envelope tests
Message envelope testing means that the MTA checks the information passed through the SMTP protocol, for example the sender and recipient information, used when transferring a message and rejects messages if they are not transmitted with valid information. Message header tests give an MTA the ability to check information stored inside of messages such as the To, From, and Date fields and to reject messages if the header is not properly formed or contains invalid information.

While these capabilities are obviously useful to eliminate spam, they ultimately guarantee only that messages are correctly transmitted and constructed, not whether they are sent by a spammer or if the message contents are spam -- thus they are not an anti-spam technology in their own right. Also problems can occur in message headers and envelopes for reasons not necessarily indicative of spam.

Simple DNS tests
Looking up sender information exchanged during the SMTP protocol using the Internet Domain Name System can be used to validate information exchanged during the SMTP protocol -- for example to check for the existence of the sender's Internet domain or the name of a machine sending messages (by looking up the name associated with the sender's Internet address).