The Bat!
Link
https://www.ritlabs.com/en/products/thebat/
“The Bat!” is a commercial email client for [Windows](…/Microsoft Windows/), by the Moldovan software company Ritlabs.
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
- 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
- Only supports [Windows](…/Microsoft 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
FAQ
Syncing the address book with Google Contacts
Alternatives
- [Claws Mail](…/Claws Mail/)