A milter is an extension to the widely used open source mail transfer agent (MTA) sendmail. It allows to add mail filters (for filtering spam, viruses ...) very efficently in the mail-processing-chain of sendmail. Milter filters can reject message during SMTP session.

Sendmail.org inludes special thread based library in sendmail distribution providing milter API. Sendmail daemon commumicates with milter process using milter protocol which is not officially documentd.

The usage of milters is spreading during the last years and milters are becoming increasingly important in mailprocessing on the large scale to block, verify and sort incoming mail.

Origin

Milter (which is short for Mail Filter) was first introduced to Sendmail in the 8.12.0-release in September 2001 and has undergone impressive improvements since then.

Interface

Sendmail provides a documented Application Programming Interface that can be used to create milters for special needs.

Milters

• MIMEDefang

External links

• www.milter.org Milter.org
• www.milter.info Milter.info
• Sendmail::Milter
• Milter protocol documentation (unofficial) - Milter API is officially documented