What is Sisimai ?

Sisimai is the successor of bounceHammer, is a Mail Analyzing Interface: a Perl module and a Ruby Gem for parsing RFC5322 bounce emails and for generating structured data such as JSON.

Sisimai v4.25.11 was released on Monday, 22 Feb, 2021. This release include updates of 60+ error message patterns, updates for text encoding, and a serious typo: of hash key in Sisimai::RFC3464 module (only in the Ruby version of Sisimai). v4.25.11 may be the final release of the version 4 series. However, we will release v4.25.12 if a serious bug were found after today. And then, Sisimai 5 and the Go language version of Sisimai are under development on sisimai/go-sisimai repository and will be released until the next summer. For further information about all the changes on this version available at blog.libsisimai.org.

Parse Bounce Emails

Sisimai is a library to parse bounce emails in a UNIX mbox file or emails in the Maildir/ directory.

Get Started

Detect Bounce Reasons

Sisimai can detect 29 bounce reasons such as "blocked", "mailboxfull", "userunknown", and so on.


Data Structure

Parsed results generated by Sisimai are converted to structured data, and could be converted to JSON.


68 Parser Engines

Sisimai can parse bounce mails from open source MTAs, commercial MTAs, and some major MSPs/ESPs.


vs. bounceHammer

On August 2014, We have started to develop a Perl version of Sisimai to resolve many fundamental problems of bounceHammer which are related to analytical precision (it could not be detected 2 or more bounces in a single email), many dependencies of external modules (some modules have not maintained for a long time), and cannot work on Perl 5.16 or later.

As of the present, the Perl version Sisimai is about 2.2 times faster than bounceHammer, have 2.0 times higher of analytical precision, depends only 2 external modules, and can work on Perl 5.10.1 or later versions of Perl. From August 2015, We have started to develop a Ruby version of Sisimai. The software has been released on Feburary 3, 2016.

Analytical Precision Ratio



The Speed Of Parsing 1000 Emails



Detectable Bounce Reasons



The Number Of MTA/MSP Modules



Dependent External Modules



Can Detect


Bounce Reasons



Engine Modules



Commercial MTA Modules



External Modules Required


The latest version is v4.25.11, released on Monday, 22 Feb, 2021.

Sisimai can run on the system that Perl or Ruby is available like the following lists, such as *BSD, Mac OS X, and Linux. Beginning of v4.22.5, Sisimai may run with ActivePerl on Windows. .

Perl Version

  • Stable version
  • Perl 5.10.1 - 5.30.X
  • CPAN

Ruby Version

  • Stable version
  • Ruby 2.1.0 - 2.7.X
  • JRuby -

Fork on GitHub

  • Development Version
  • p5-sisimai (Perl)
  • rb-sisimai (Ruby)


Anyone can use Sisimai because it is an Open Source Software, however, we, Cubicroot Corporation Limited (a development company of Sisimai) is ready to support your installation of Sisimai, development of relevant scripts, data management of parsed bounces on RDBMS, operations on your system for continuous management of email bounces, and a migration from bounceHammer.

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