Email::Sender::Transport is a Moo role to aid in writing classes used to send
mail. For the most part, its behavior comes entirely from the role
Email::Sender::Role::CommonSending, which it includes. The important
difference is that Transports are often intended to be used by
Email::Sender::Simple, and they provide two methods related to that purpose.
First, they provide an allow_partial_success method which returns true or
false to indicate whether the transport will ever signal partial success.
Second, they provide an is_simple method, which returns true if the
transport is suitable for use with Email::Sender::Simple. By default, this
method returns the inverse of allow_partial_success.
It is <B>imperativeB> that these methods be accurate to prevent
Email::Sender::Simple users from sending partially successful transmissions.
Partial success is a complex case that almost all users will wish to avoid at