Shortcut - Select Messages from the Same Sender - Airmail for macOS
Click on a message to identify a sender.
Press the equal sign "="
All the message in the list with the same sender will be highlighted in grey.
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You can easily notice in the message list above that - notifications@... is the sender of which all messages
are highlighted here.
Press the equal sign "="
All the message in the list with the same sender will be highlighted in grey.

You can easily notice in the message list above that - notifications@... is the sender of which all messages
are highlighted here.
Updated on: 02/28/2019
Thank you!