Note:
A Respond Later feature can be applied to a received message.
The red colored-dotted circle which appears besides message denote this feature.
Click on the message-right-click-menu as directed by the arrow, shown from the figure below.
A message-right-click-menu is opened.
Select Respond Later as directed by the arrow, from the figure below.
Respond Later is applied. Find the red colored dotted circle beside the message as shown in the figure below.
Note:
The applied Respond Later gets auto-cleared when a message is replied.
Or, you can manually clear the applied Respond Later from Message-Right-Click-Menu.