All sorts of files can be attached to emails, such as word processor documents, audio and music, video clips, PDFs and images. If you scan through your email messages in Mail you will see that some attachments appear as icons and others appear within the message body. It all depends on the type of file.
Mail displays the actual file contents whenever possible and the most obvious type of file to do this with is JPEG photos and other image types. If someone sends you an email with a photo attachment, you can see the photo in the message. The same is true of PDF files too. If you get a PDF document, you can see it within the email message body. There is no need to save it to disk and load it into an app to view it. Other file types, such as anyfile.xyz, are just displayed as an icon when Mail doesn't know how to handle them.
The default for Mail is to display images and PDFs within the message
The question is, would you prefer all file types to be displayed as an icon? When you get a lot of emails each day and are sorting through them, it may be more convenient and quicker to avoid displaying attachments. You can deal with them later.
To stop mail showing attachments within messages and to show them as an icon, go to the Applications/Utilities folder and open Terminal. At the command prompt, enter the following:
defaults write com.apple.mail DisableInlineAttachmentViewing -bool YES
If you want to put things back as they were and show attachments within email messages whenever possible, return to Terminal and type:
defaults write com.apple.mail DisableInlineAttachmentViewing -bool NO
The Terminal command causes images to appear as icons. Click and press spacebar to view them
What these commands do is to write a value to the Mail preferences file. They create a value called DisableInlineAttachmentViewing, set the type to boolean (a yes/no, off/on value) and set it to YES or NO. Mail reads the preferences file when it starts up and takes note of values stored in it.
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