Ritlabs The Bat! Professional Edition v7.2

The very best secure email client software. Continuously improving since 1998!
The Bat! is a secure email client software, built to protect your correspondence against third-parties.
The Bat! protects your information through multiple encryption streams with the option to encrypt your emails on a disk and during communication through an SSL/TLS connection. Free from global email providers that keep your messages in the cloud, and free from Web clients, The Bat! ensures your data stays private.
The Bat! mail client is able to process and store an unlimited number of messages and has no restriction on the number of email accounts you can use.

Key Features
PGP, GnuPG and S/MIME Support
Powerful Filtering System
Internal HTML Viewer
The Bat!'s own Address Book
Safe Handling of Attached Files
Handy Templates
Selective Download
RSS Feed Subscriptions
 
https://www.ritlabs.com/en/products/thebat/