Complete release notes can be found in the project’s GitHub releases page.
Anymail practices semantic versioning. Among other things, this means that minor updates (1.x to 1.y) should always be backwards-compatible, and breaking changes will always increment the major version number (1.x to 2.0).
PRE-1.0 DEVELOPMENT VERSIONS
Anymail is under active, early development right now. Prior to a 1.0 alpha, features and APIs may change rapidly. (Per semver, the 0.x minor version will get bumped for any breaking changes before 1.0.)