Reply via e-mail to epic discussion is discarded

Steps to reproduce

• subscribe to epic
• wait for comment from other user
• reply via e-mail with attachments

What is the current bug behavior?

E-mail is silently ignored.

What is the expected correct behavior?

New comment is created with attachments added to the Markdown.

Possible fixes

My guess is this is happening because of ReplyProcessing assuming we are in a project context while epics live in a group context.