## 7.1.8 Exception and Defect classes

The following exception classes are defined in the `email.errors` module:

exception `MessageError`( | )

  This is the base class for all exceptions that the `email` package can raise. It is derived from the standard `Exception` class and defines no additional methods.

exception `MessageParseError`( | )

  This is the base class for exceptions thrown by the `Parser` class. It is derived from `MessageError`.

exception `HeaderParseError`( | )

  Raised under some error conditions when parsing the RFC 2822 headers of a message, this class is derived from `MessageParseError`. It can be raised from the `Parser.parse()` or `Parser.parsestr()` methods.

  Situations where it can be raised include finding an envelope header after the first RFC 2822 header of the message, finding a continuation line before the first RFC 2822 header is found, or finding a line in the headers which is neither a header or a continuation line.

exception `BoundaryError`( | )

  Raised under some error conditions when parsing the RFC 2822 headers of a message, this class is derived from `MessageParseError`. It can be raised from the `Parser.parse()` or `Parser.parsestr()` methods.

  Situations where it can be raised include not being able to find the starting or terminating boundary in a multipart/* message when strict parsing is used.

exception `MultipartConversionError`( | )

  Raised when a payload is added to a `Message` object using `add_payload()`, but the payload is already a scalar and the message's Content-Type: main type is not either multipart or missing. `MultipartConversionError` multiply inherits from `MessageError` and the built-in `TypeError`.

  Since `Message.add_payload()` is deprecated, this exception is rarely raised in practice. However the exception may also be raised if the `attach()` method is called on an instance of a class derived from `MIMENonMultipart` (e.g. `MIMEImage`).

Here's the list of the defects that the `FeedParser` can find while parsing messages. Note that the defects are added to the message where the problem was found, so for example, if a message nested inside a multipart/alternative had a malformed header, that nested message object would have a defect, but the containing messages would not.

All defect classes are subclassed from `email.errors.MessageDefect`, but this class is not an exception!

New in version 2.4: All the defect classes were added.

- `NoBoundaryInMultipartDefect` - A message claimed to be a multipart, but had no boundary parameter.

- `StartBoundaryNotFoundDefect` - The start boundary claimed in the Content-Type: header was never found.

- `FirstHeaderLineIsContinuationDefect` - The message had a continuation line as its first header line.

- `MisplacedEnvelopeHeaderDefect` - A ``Unix From'' header was found in the middle of a header block.

- `MalformedHeaderDefect` - A header was found that was missing a colon, or was otherwise malformed.

- `MultipartInvariantViolationDefect` - A message claimed to be a multipart, but no subparts were found. Note that when a message has this defect, its `is_multipart()` method may return false even though its content type claims to be multipart.