Lots of new features, but a few API changes (thus the MAJOR version change).
Basics are:
Network Delivery classes are no longer singletons, each instance of Mail can have it's own delivery method
Attachments are just parts and have an awesome API
Mail default values for address fields can be modified
Can access raw address objects directly from the header fields
Many bug fixes.
Check it out at
Installation is:
gem install mail
Mikel