Mobile read mail disappearing, despite settings set to not delete

Mobile read mail disappearing, despite settings set to not delete

I have a problem that when I read mail on my android device, it disappears from my Zoho mail server.  It does not go to Trash, Inbox, or Spam; it is just gone from the server. 

I verified that my desktop application's POP and IMAP settings do not delete from the server, but cannot find a similar setting in the mobile application.  If the desktop IMAP settings do not apply to the mobile, where are they?  I do not find anything server related in the gear icon or in app manager....