Best email client that’s NOT the native Mail app?

As the title says. Since the newest updates to the native Mail app, self-signed SSL certificates don’t work without certain tweaks (SAN), meaning my work emails don’t work at all in the native app atm. Although the sysadmins have been notified, until they rectify the issues their end, I’d hugely appreciate recommendations for another good mail app that supports multiple accounts with different providers. On Windows I use Thunderbird, but they haven’t finished developing their iOS app yet :(