Emails from the rfc/ legacy/ malformed/ and thirdparty/ folders were imported from this repository:
https://github.com/stalwartlabs/mail-parser
Specific COPYING files are available in each folder to trace their authors.
If nothing is stated in these folders, the following copyright applies: Copyright (C) 2020-2022, Stalwart Labs Ltd.
And the distribution license is either BSD-2, MIT or Apache 2.