Most non-multipart type messages are parsed as a single
message object with a string payload. These objects will return
False for is_multipart(). Their
get_payload() method will return a string object.
All multipart type messages will be parsed as a
container message object with a list of sub-message objects for
their payload. The outer container message will return
True for is_multipart() and their
get_payload() method will return the list of
Message subparts.
Most messages with a content type of message/*
(e.g. message/delivery-status and
message/rfc822) will also be parsed as container
object containing a list payload of length 1. Their
is_multipart() method will return True. The
single element in the list payload will be a sub-message object.
Some non-standards compliant messages may not be internally consistent
about their multipart-edness. Such messages may have a
Content-Type: header of type multipart, but their
is_multipart() method may return False. If such
messages were parsed with the FeedParser, they will have an
instance of the MultipartInvariantViolationDefect class in their
defects attribute list. See email.errors for
details.
