Milter

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The Milter (portmanteau for mail filters ) is an extension of the widely used mail-dispatching mail -mail (MTA), Sendmail and Postfix. This allows administrators to add email filters to filter spam or viruses in mail processing chains. In the language of art, "milter" refers to the protocol and API that implement the service, while "milter" has referred to the filter application that uses the milter to provide services.

Video Milter

Histori

Prior to the advent of the milter, email filters were generally implemented as programs that the MTA would submit messages after it actually arrived, with most of the information the message envelope was removed. The program can then analyze the header and message content and make the decision to receive the message (ie return the "success" status to the MTA) or reject it (ie return the "failed" status to the MTA). The MTA will then record a successful delivery or return a failure message to the sender as appropriate, and the filter will be responsible for affecting the delivery of messages (to the intended inbox, as is, or modified to remove unwanted content, or to a specific folder, etc..).

A lighter MTA capable of telling the connected filter about each message delivery phase, from the initial client connection through the transmission settlement. In each SMTP session phase, filters are given data about messages that arrive and then have an opportunity to end the reception of messages earlier when needed. For very large messages, this can have a huge impact when the decision to decline can be made as early as possible. In addition, unlike previous models, MTAs that have more power can connect to multiple filters in parallel that serve certain purposes such as anti-virus, anti-spam, message authentication, flow settings, etc. Finally, the filter can take special action on messages: add or remove recipients in envelopes; changing body before delivery; add, change, or delete header fields in messages, etc.

The Sendmail Consortium includes a dedicated threaded library in sendmail distribution that provides lighter APIs.

Military usage has spread in recent years and milters are becoming increasingly important in large-scale mail processing to block, verify and sort incoming mail.

Maps Milter

MTA

Sendmail

Milter was first officially introduced to Sendmail 8.12.0 released on September 8, 2001. Milter is available in sendmail version 8.11.x as FFR (For Future Release/Beta code). Milter has undergone substantial improvements since its first official release. The latest information is at SENDMAIL RELEASE NOTES to find out about Milter related changes in the sendmail version. Postfix

Military support added to Postfix 2.3.0 was released July 12, 2006. Many, but not all, milter can be used with Postfix "out of the box".

Postoffice SMTP Server

The post office got lighter support since the 1.3 release.

src: miltera.com

Interface

The Sendmail Consortium provides a documented Application Programming Interface that can be used to create special-purpose milter. Library provided by The Sendmail Consortium based on pthread. However, documentation of the protocols used for communication between sendmail and lighter processes is not provided. This internal protocol may change in the new sendmail version.

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Sample Milters

• MSH Autoresponder
• MIMEDefang
• j-chkmail
• milter-graylist
• WhoIs Milter Prefix
• milter-regex - Deny a letter that matches a regular expression
• bogofilter-milter
• OpenDKIM

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References

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External links

• "Developer Center". milter.org . Archived from the original on 2012-10-25. Ã ,
• "Interactive catalog of sendmail email filters". milter.org . Archived from the original in 2015-05-10.
• SMTP postoffice server

Source of the article : Wikipedia