On December 21, 2001, a version incorporating support for SpamAssassin was released, making MIMEDefang a filter for both spam and viruses.

Skoll's company, Roaring Penguin Software, developed and sold a commercial anti-spam product known as CanIt, which is based on the open-source version of MIMEDefang.

[citation needed] On March 5, 2020, AppRiver agreed to give The McGrail Foundation leadership of the open-source MIMEDefang project[4] for a period of three years, automatically renewable for one-year terms after that unless either AppRiver or The McGrail Foundation chooses not to renew the agreement.

[citation needed] The Milter library included with Sendmail uses POSIX threads to allow multiple concurrent filters.

It includes convenience routines for parsing and rebuilding MIME messages so that filter authors can concentrate on high-level policy rather than worry about low-level API details.