UploadFile mimetype & name mangling

[foarsitter]

When using a UploadFile as an attachment the file_meta is always None. This happens during the validation of MessageSchema:

fastapi-mail/fastapi_mail/schemas.py

Line 52 in a4aff1a

def validate_file(cls, v):

In my opinion MailMsg.attach_file should be extended to support UploadFile and derive the mimetype from the content-type header.

content_type = file.headers.get("Content-Type", "application/octet-stream")
_maintype, _subtype = content_type.split("/")
part = MIMEBase(_maintype=_maintype, _subtype=_subtype)

When extending the FastMail class I discovered the usage of double underscored methods. What is the reason of applying name mangling here? In order to override __prepare_message I have to name the method _FastMail__prepare_message and that is not something I'm enthusiastic about ;)

class ExtendedFastMail(FastMail):
    async def _FastMail__prepare_message(