amavisd-new operates as an SMTP proxy, designed to hook in to the content_filter mechanism of Postfix. (amavisd-new also supports Sendmail through its Milter interface and in a dual-server configuration and Exim using it as an SMTP proxy.) amavisd-new is written, maintained, and supported by Mark Martinec of the Jozef Stefan Institue in Slovenija and is aided by an active user community. It began as a fork from amavisd, a daemonized version of the AMaViS scanner, which was one of the first open source mail virus scanners. The modern amavisd-new scarcely resemebles its predecessor and improves upon it considerably, while a difference of philosophies has prevented amavisd-new from being merged back into amavisd or simply taking over as the official scanning engine of the AMaViS project. That should not sound like a euphemism for saying that either Mark or the developers of the original AMaViS have overbearing personalities; Mark himself is helpful and personable on the amavis-users mailing list, and the original AMaViS folks have been quite tolerant of the amavisd-new traffic on their list, which these days accounts for at least half.

amavisd-new is written in Perl, and takes advantage of a number of Perl modules, such as the Net::Server module, which it uses to implement a robust forked parent/child environment, and Mail::SpamAssassin, the core scanning engine of SpamAssassin, so it does not need to use 'spamd'.

Mark strives to make amavisd-new adhere to standards and as the result is a well-regarded and standards-friendly system. It is also fast, although as a Perl application it can use a considerable amount of memory, so it is best limited to a few child processes. As amavisd-new is very flexible, the myriad of options makes it intimidating to configure.

amavisd-new is able to reliably deliver messages because it never has to store the messages itself; as soon as the Postfix sending process connects to amavisd-new, amavisd-new connects to the Postfix receiving process and does not send an acceptance response to the sending process until the receiving process has also accepted the message. Should the receiving process fail, amavisd-new will return a status code to the Postfix sending process and Postfix will maintain the message in its queue until the problem is rectified.