Python module for generating email authentication headers: Authheaders can
generate both authentication results header fields and DKIM/ ARC signatures.
It can perform DKIM, SPF, and DMARC validation, and the results are packaged
into a single Authentication-Results header. It can also DKIM and ARC sign
messages and output the corresponding signature header fields.

Homepage:
https://github.com/ValiMail/authentication-headers
