The Bat!
https://www.ritlabs.com/en/products/thebat/
“The Bat!” is a commercial email client for Windows, by the Moldovan software company Ritlabs.
Review
Section titled “Review”I have been using The Bat! on and off since 2012 and probably years before that, but that’s how far back I have saved my licenses.
Positive
Section titled “Positive”- Can handle large mailboxes easily
- Supports PGP and S/MIME
- Portable mode (e.g. run from a flash drive)
- Extensive filtering and automation (rules) options
- Very customizable
- Secure HTML view
- Integrated RSS reader
Negative
Section titled “Negative”- Only supports Windows
- Not open-source (could cease to be developed)
- Stability has gone down-hill the last couple of years/versions
- “Use it or leave” attitude by support staff
Syncing the address book with Google Contacts
Section titled “Syncing the address book with Google Contacts”Alternatives
Section titled “Alternatives”- Claws Mail