This update for enigmail to version 2.0.4 fixes multiple issues.

Security issues fixed:

- CVE-2017-17688: CFB gadget attacks allowed to exfiltrate plaintext out of encrypted emails.
  enigmail now fails on GnuPG integrity check warnings for old Algorithms (bsc#1093151)
- CVE-2017-17689: CBC gadget attacks allows to exfiltrate plaintext out of encrypted emails (bsc#1093152)

This update also includes new and updated functionality:

- The Encryption and Signing buttons now work for both OpenPGP and S/MIME.
  Enigmail will chose between S/MIME or OpenPGP depending on whether the keys
  for all recipients are available for the respective standard
- Support for the Autocrypt standard, which is now enabled by default
- Support for Pretty Easy Privacy (p≡p)
- Support for Web Key Directory (WKD)
- The message subject can now be encrypted and replaced with a dummy subject,
  following the Memory Hole standard forprotected Email Headers
- keys on keyring are automatically refreshed from keyservers at irregular intervals
- Subsequent updates of Enigmail no longer require a restart of Thunderbird 
- Keys are internally addressed using the fingerprint instead of the key ID