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How are versions numbered?

SpamAssassin uses a version numbering scheme modelled after the one used for Linux kernels. Versions are denoted using a standard triplet of integers: MAJOR.MINOR.PATCH. The basic intent is that MAJOR versions are incompatible, large-scale upgrades of the API. MINOR versions retain source and binary compatibility with older minor versions, and changes in the PATCH level are perfectly compatible, forwards and backwards.

• The major version number , currently at zero, increments upon significant architectural changes or the achievement of important milestones in capabilities. The minor/mode version number increments as progress is made within a major version, with the added constraint that:
• all external releases have an even minor/mode version number (e.g., 3.0.0)
all internal/development versions have an odd minor/mode version number (e. g., 3.1.0)

• The patchlevel number increments for small sets of changes, providing the most fine-grain timeline of software evolution. Patchlevels increment regularly for internal/development(odd minor level) work, but only increment for external releases when an official update to the previous release version has been tested and packaged.
  

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