In order to easily distinguish between useful Mail and useless Mail from your cluster of messages inside Mail, you can use four types of message marking as your assistance. These four types of marking available in Mail are: Mark As Unread, Mark As Flagged, Mark As Junk Mail and Mark As Hidden.

How to use these four message markings for your Mail?

Mark As Unread

Unread messages are indicated by blue dot next to the messages. Usually, the message will be automatically set as read the time you open the message. Sometimes you will need to remind yourself to review the message again, that's when Mark Message As Unread comes into play. After marking the message as unread, the blue dot will reappear again.

Shortcut to Mark As Unread: U.

Mark As Flagged

There is a time when you feel you will need particular message in your inbox as future reference or maybe you happen to read an article from RSS of UsingMac.com and think that you will need it again in the future, I recommend you to Mark It As Flagged. Flagged message, in the future, can be sorted up by clicking on the flag button and results in flagged messages appear before other unflagged messages.

Shortcut to Mark As Flagged: L.

Mark As Junk Mail

If you happen to see messages highlighted in brown color instead of black, it means that those messages are junk. Most of the time, your server junk mail filter can determine for you which message is junk and which is not. But in case these junks still be able to infiltrate your inbox, you need to mark it as junk to throw the message away to junk mailbox.

If your server is IMAP, you want to separate your junk mailbox from inbox, you can do the following steps:

1. Go to Mail Preferences Pane
2. Click on Junk Mail section
3. Enable junk mail filtering
4. And choose Move it to the Junk mailbox
5. You will see new mailbox appear on your Mail.app labelled Junk

Shortcut to Mark As Junk Mail: J.

Mark As Hidden

Actually, there is two ways to do this, depend on for what purpose you want to hide your messages for.

If you want to hide your messages because you don't want to see your inbox overflowed by messages other than unread messages; You can do the followings:

1. Highlight all unread messages
2. Choose View ▸ Display Selected Messages Only
3. All other messages will be hidden, unless for those selected messages
4. To unhide those hidden messages, choose View ▸ Display All Messages

The second way, if you want to hide your deleted messages instead of moving them to other folder, you can follow these simple steps:

1. Go to Mail ▸ Preferences..
2. Click on Accounts section
3. Untick the checkbox next to Trash
   This checkbox says something like, "Move deleted messages to a separate folder".
4. Hence, instead of being moved to Trash folder, your deleted messages will stay hidden in your inbox
5. Your deleted messages will look as if they're being moved to another folder, but actually when you perform Show Deleted Messages (L) they will appear in their ethereal form

Shortcut to Mark As Hidden (Deleted): .