(From http://ecentryx.com/gems/mime/)

    2008-11-05, v0.1

        First public release.

    2013-12-18, v0.2.0

        Update for Ruby 1.9.3.

        Update Rakefile test, package, and rdoc tasks.

        Change test suite from Test::Unit to Minitest.

        Cleanup existing and add new tests cases.

        Clarify code comments and README examples.

        Fix content type detection.

    2014-02-28, v0.3.0

        Simplify API of DiscreteMediaType subclasses.

        Disallow Content-Type changes after instantiating DiscreteMediaType.

        Add flowed format support for text/plain (RFC 2646).

    2014-04-18, v0.4.0

        Major API disruption!

            Rename classes:

                HeaderContainter => Header

                remove “Media” suffix from the 5 DiscreteMedia and 2 CompositeMedia subclasses. See commit for details.

                MIME::Message => MIME::Mail

            Rename methods:

                remove “_entity” suffix from add, inline, and attach in CompositeMedia.

                remove “content_” prefix from id, disposition, description, and transfer_encoding in Headers::MIME.

            Remove methods:

                Header#add

            Add methods:

                Header#set (replace Header#add)

                Header#get

                Header#delete

            Reverse order of entities in CompositeMedia::Body, which most likely reverses all CompositeMedia add, inline, and attach method calls. See commit for details.

        Other changes

            Use From header field domain in the Message-ID header.

            Add more randomness when generating header IDs.

            Header field names are now case-insensitive to comply with RFCs.

            Accept String, Array, and Hash for originator and destination mailboxes.

            Add CompositeMedia::Body class for nesting MIME entities.

            Improve docs and examples for Content-Disposition (inline/attachment).

            FIX: remove trailing CRLF in Mail#to_s and update tests.

            Add README links to message lint tools on IETF.org.

            Add Send, In-Reply-To, and References RFC 5322 header fields.

            Comply with RFC regarding parameter quoting in header field bodies. I.e., do not quote atom/dot-atom parameter values.

            Many fixes and improvements in code, tests, documentation, and examples.

    2014-04-20, v0.4.1

        Add bug tracker URL.

        Link to referenced commit messages.

    2014-06-13, v0.4.2

        FIX: remove header field when set to nil.

        RFC compliance: set Sender field to first From address if multiple From addresses and the Sender header is not already set.

        Improve TextFlowed tests.

        Add TODO.mkd.

        FIX: Ruby 1.8.7 compatibility issue.