EmailMessage.as_string is altering the message state and actually fix bugs

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-06-28.09:43:33.284>
labels = ['3.8', 'type-bug', '3.7', 'expert-email']
title = 'EmailMessage.as_string is altering the message state and actually fix bugs'
updated_at = <Date 2020-07-10.16:58:06.348>
user = 'https://github.com/mardiros'

bugs.python.org fields:

activity = <Date 2020-07-10.16:58:06.348>
actor = 'r.david.murray'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2020-06-28.09:43:33.284>
creator = 'mardiros'
dependencies = []
files = ['49271']
hgrepos = []
issue_num = 41145
keywords = []
message_count = 2.0
messages = ['372508', '373472']
nosy_count = 3.0
nosy_names = ['barry', 'r.david.murray', 'mardiros']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41145'
versions = ['Python 3.7', 'Python 3.8']