You can perform custom functions (“actions”) on messages and their attachments. For a general discussion on how to define your own, see see Actions.
mu4e-view-action (a) lets you pick some custom action to
perform on the current message. You can specify these actions using the variable
mu4e-view-actions; mu4e defines a number of example actions.
Similarly, there is
mu4e-view-attachment-action (A) for
actions on attachments, which you can specify with
mu4e predefines a number of attachment-actions:
emacs(e): open the attachment in your running
emacs. For example, if you receive some text file you’d like to open in
emacs: A e 1 RET.
These actions all work on a temporary copy of the attachment.