Whilst browsing the navigation, I feel that it would make more sense to use the Inbox/Calendar next to the 3 lines on the left to navigate within that tab. So for example, select the three lines and select Mail. Then select Inbox (next to the three lines) to change the email folder and navigate the email subfolders that way.

The same could be done for calendars or contacts. You could select Calendar or Contacts under the Three Lines and then next to the three lines click on Calendars or Contacts to select/unselect or view specific Contact Folders or Calendars. It just feels logical to want to click inbox to change the email folder to a subfolder. In addition, it would make it more consistent with the desktop version of Mdaemon Webmail where you only have the main Tabs Email, Calendar, Contacts etc on the LHS menu and then in the next vertical section you can choose the calendars/email folders etc.

I feel that having the main tabs Emails, Contacts, Calendars in the same view as the list of calendars, contact folders or email folders makes it more cluttered. The 3 lines should be used to select the main tabs Email, Calendar etc, not to navigate within the tab.

Hope this feedback helps. I really like the new mobile theme otherwise.