Steps to reproduce the issue

Forked from #34233 (comment)

@brianteeman The more I look at this the more I ask myself what is the point of the filename field. What purpose does it serve? What is the usecase that it satisfies

The additional oversight is that placeholders cannot be used in the name field, like they can in the mail body/subject.

Thinking how this feature might be used, the 3pd might want to add dynamic detail to the file name. E.g Joe Blogs buys an ebook, and so the filename becomes Order123_Bloggs_book.pdf dynamically using the placeholders.

Expected result

Attachment name parsed for placeholders that can be replaced

Actual result

Attachment name currently not parsed for placeholders that can be replaced