import email.parser
import email.policy

email_str = '''\
Date: 01 Jan 2001 00:01+0000
From: arthur@example.example
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary=autocracy

--autocracy
Content-Type: text/plain

By hanging on to outdated imperialist dogma which perpetuates the economic and
social differences in our society.

--autocracy
Content-Type: text/html

<html><body><p>By hanging on to outdated imperialist dogma which perpetuates
the economic and social differences in our society.</p></body></html>

--autocracy--
'''

full_parser = email.parser.Parser(policy=email.policy.default)
parsed_email_full = full_parser.parsestr(email_str)
print(parsed_email_full.defects)  # Prints [] as expected

header_parser = email.parser.HeaderParser(policy=email.policy.default)
parsed_email_headers_only = header_parser.parsestr(email_str)
print(parsed_email_headers_only.defects)  # Prints [MultipartInvariantViolationDefect()]