XnView MP stands for Multi Platform = it is available for Windows, Linux and MacOS. It is a continuation of the older XnView Classic. In my opinion it is a great alternative to Windows photos app or any Linux image viewer that comes preinstalled. I even think it is an alternative to IrfanView. It is really fast and simple to use, supports more than 500 image formats, has built in folder browser, image converter, editor... AND MORE!
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.