I tried doing a naive implementation (just checking for \n or \r in the argument to Header) but that breaks a lot of unit tests. For example the test message msg_16.txt contains a header like this:

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in other words the header is split up by \n\t. I'm not very familiar with the RFCs, is there some smart way to do this? (This is my first attempt to contribute to Python btw!) It seems many tests rely on this "bug" in Header.