Overall, it works well and does so without the overhead of Moose. My only gripe: the use of 'use parent'. There is nothing in this module that requires the use of 'use parent' over 'use base'. As such, this is an example of change for the sake of change rather than change for the sake of necessity. Many of us do not have control over when we can upgrade to a later version of Perl. Were 'use base' used instead, I'd give it straight 5's.
The documentation for this module is poor. He simply provides an example with no documentation on the functions, classes, etc. in the module. Additionally his example uses an irrelevant framework called Dancer, distracting a potential user from the task at hand.
The package itself is very capable and does pretty much anything you throw at it. That said, the documentation leaves a lot to be desired. Too much emphasis is placed on the internal details of how it works as opposed to simply giving a "black box" view of how to accomplish your goal. For example, a clear way of creating a POP3 mailbox accessor isn't provided until several pages down in the documentation on the POP3 module. It should be, IMO, at the very top of it.
Log4j was introduced to the world as a great example of how to over-engineer a very trivial problem. This module has brought that same level of needless complexity to perl. In a nutshell, this module uses 1.3MB of code to accomplish the most common usage scenario: conditionally appending a single line of text to a file. Additionally, the construction process can be needlessly complicated.
The poor rating isn't so much for the module itself, but rather these modules all together. My gripe is with the bundling. Rather than bundling a set of similar modules together, instead many minor modules are distributed separately creating in effect a 'DLL Hell' or in this case 'PM Hell'. This package is a great example. Prerequisites include:
Rolling these together into a single Email module would make far more sense and make distribution far easier for someone who has to actually install these and doesn't have the luxury of the CPAN module for use with installation.