Set to 10 from admin.
From user end after 9 attachments it gives error message on attaching 10th one.
You are only allowed to have 10 attachments.
This is on 2.2RC1 The image file attached. Even the Template::dump shows 9 attachments. (nessa derivative template)
Also though the attachments are cleaned up, but the directories in which these attachments are under upload never gets deleted from server.