Change Viewing settings in Mail on Mac
Use Viewing settings in Mail to change options for viewing messages.
To change these settings in the Mail app on your Mac, choose Mail > Settings, then click Viewing.
Choose the number of lines of the message to show in the message list.
Move discarded messages into
Choose where to move messages when you swipe left on them in the message list—to the Trash mailbox to delete them or to the Archive mailbox to archive them.
This setting also determines whether you can delete or archive messages from Mail notifications.
Show message headers
Choose to show default or custom fields in message headers.
To add fields, click the pop-up menu, choose Custom, click the Add button , then enter the name of a message header, such as Return-Path.
Display unread messages with bold font
In column layout, show unread messages in bold to help distinguish them from messages you have read.
Use Smart Addresses
Show recipients’ names but not their email addresses (if a recipient is in the Contacts app or the Previous Recipients list, or on a network server).
Use dark backgrounds for messages
Show messages in the preview area and new messages you’re writing with either a dark background (select the checkbox) or a light background (deselect the checkbox). This option is available only if you set Appearance to Dark in Appearance settings.
When this checkbox is selected, you can switch to a light background while viewing or writing a message. Choose View > Message > Show with Light Background. To show the message with a dark background again, choose View > Message > Show with Dark Background.
Highlight messages with color when not grouped
When email conversations are turned off, highlight the messages in a conversation in the message list, to help identify them more easily. Click the color well to choose a highlight color.
Include related messages
When viewing a conversation, show related messages (those located in other mailboxes).
Mark all messages as read when opening a conversation
Mark all unread messages in a conversation as read when you view the primary message of the conversation.
Show most recent message at the top
Display the most recent message in a conversation first in the preview area. If the checkbox is deselected, the oldest message appears first.
You can sort, filter, and otherwise change how messages appear in the message list.