Postbox

vs

Yandex.Mail

K-9 Mail is an open source email client focused on making it easy to chew through large volumes of email. K-9 Mail is designed for both novice and power users and offers lots of features for everyone. It provides features like Push IMAP Support, GPG & PGP/MIME support, Per Account Notifications, Unified Inbox, White and Dark Theme, and Signatures.

Zoho Mail provides ad-free email hosting for business and organizations. It's comes with intuitive migration tools, along with 24/7 dedicated migration support to ensure smooth, lossless migration from your existing email provider. With Zoho Mail, your organization can manage all their email, calendar and contact needs. Since Zoho Mail is part of the Zoho's suite of online productivity, it's easy to extend the capability in to more parts of Zoho's offering and essentially run your entire business with Zoho. Zoho is provided as a Freemium software, where the free plan supports up to 5 users in an organization.

Apple Mail is email client built specifically for the Apple eco-system. You can use Apple Mail on your mobile iOS device or your macOS desktop or laptop. It provides all the features needed to communicate effectivley via email, such as view and manage your favorite mailboxes right in the Mail sidebar, search for emails, it's easy to see which mailboxes are being searched and quickly select different mailboxes, easily view and sort messages in column layou and quickly open and use tabs in the Mail window.

Arguably the most popular email service in the world, Gmail provides a email inbox for over 1.5 billion users. With Gmail you can create an email account for free that manages emails and contacts in the same application. Gmail is web-base but provides clients for mobile devices and supports third-party programs that synchronize email content through POP or IMAP protocols.

A free an open-source email client developed openly by the Mozilla Foundation and the community. Thunderbird is easy to setup and customize and supports POP and IMAP. The email client comes with all features needed to search, filter, write and manage emails, but also have builtin support for live chat between contact and RSS/Atom feed reader.

World's largest secure email service providing end-to-end encrypted email accounts. ProtonMail is based in Geneva, Switzerland and protected by Swiss privacy laws. The software is openly developed with fully open source code.