The email.errors module has various error classes which are not in the stubs:

https://github.com/python/cpython/blob/master/Lib/email/errors.py
https://github.com/python/typeshed/blob/master/stdlib/3/email/errors.pyi

However, at least some of those don't actually seem to be documented:

https://docs.python.org/3/library/email.errors.html

Should those be in the stubs? Is it perhaps a Python bug that those aren't documented?