Please add an option for including attachments when replying. That option is available when forwarding, but often the attachments need to be maintained for documentation when replying and BCCing oneself.
Attachment to Reply" is a peculiar case, but a simple one. Just press "Reply" and on the message screen that opens, select the file you want to attach from "Attach" shown at the top. Replies with attachments take a little longer to send.