What is the Messaging Classic application, how does it work?

According to the introduction of DC Mobile Dev Team, Messaging Classic is a Communication app on the Android platform. There is currently a 1.7.8 version released on Feb 14, 2020, you can see the details below.

Message Classic (alternate name as Messaging Classic) is the stock messaging (SMS & MMS) app ported from the Android native system!

Most of the phone manufacturers, for example, Samsung, LG, Sony and HTC, build their own messaging apps with different user experience, Message Classic brings you the native taste with Google design.

In Nexus 5, Google Hangouts is the default messaging app, while the original messaging app is gone. Message Classic gives you a chance to bring it back.

Remember to disable your other third party SMS apps' notifications or you may get duplicated notifications for each message.

Highlights:
• Totally free.
• Fully support Android 4.4.
• Fully support MMS for all Android versions.
• Quick reply pop-ups
• Quick action button support in message notification

In Android 4.4, an SMS app can not update SMS/MMS data if it's not the default SMS app. So please set Message Classic as your default SMS app.