To perform actions on all messages in the thread, such as deleting, archiving, or tagging them:
1.In the Message List, collapse the thread by clicking ⌄ at the bottom of the original message.
2.In the context menu of the thread, select the desired command or press the button, for example,
Delete Selected Messages.

You can still perform actions on individual messages by expanding the thread using the > button at the bottom of the original message and selecting the desired message.