To remind yourself to follow up on a message, you can add a follow-up flag. A flag gives you a visual cue that you want to return to that message later. In the message list, flagged items display the symbol.
Pinning a message moves it to the top of your inbox so it's easy to find later. A pinned message is indicated by a symbol.
Flag a message
In the message list, hover over the message to see the flag option.
Select to flag the message.
Select to unflag the message.
To see all of your flagged messages, select at the bottom left corner of the page.
Pin a message
Note: To pin a message or see pinned messages, your inbox must be sorted by date. Select Filter at the top of the message list to change how your inbox is sorted.
In the message list, hover over the message to see the pin option.
Select to keep the message at the top of your inbox.
Select to unpin the message.