Email::Abstract provides module writers with the ability to write
representation-independent mail handling code. For instance, in the
cases of Mail::Thread or Mail::ListDetector, a key part of the code
involves reading the headers from a mail object. Where previously
one would either have to specify the mail class required, or to
build a new object from scratch, Email::Abstract can be used to
perform certain simple operations on an object regardless of its
underlying representation.

WWW: https://metacpan.org/release/Email-Abstract