1
defaults write com.apple.mail DisableInlineAttachmentViewing -bool yes

It is related to this question:

How can I disable inline attachment previews (i.e. view as icon by default) in Mac Mail in macOS Mojave?

2

When you’ve written a boolean value, you can choose to write the opposite value, replacing yes with no. Usually, to reset a preference, you delete the preference so the default takes effect, which you can do with defaults delete:

defaults delete com.apple.mail DisableInlineAttachmentViewing
  • Thank you GRG, but now I need to know what's the difference between Revert and Delete. The mentioned command was posted as answer on the original question, but this command displays the attachment as icon only during email composing, in the sent items the attachment is fully displayed... – user331543 Mar 22 at 9:13
  • @1252 - there is no "revert" command. When you "delete" whatever the setting was changed to reverts back to what it was from the factory. – Allan Mar 22 at 17:02

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