Hi
I am not aware of any possibility to directly manipulate the attachment file names at download.
But you could set up a job with:
1: an "Email - Get headers" task, that fetch subject names of the relevant mails for download.
2: a loop on the output of 1 with:
a: an "Email - Get messages" task (that downloads the attachments)
b: a file rename task where you could add the subject to the file names.
In the loop settings you use """ as text qualifier. Choosing column 2 you then get the subject in the variable {LOOP(CurrentValueX)}. This might be relative to the output of the specific mail server.
Hope that helps.