Comment 0 for bug 1664098

This would only occur if unity-mail was never set up using an eariler version. Last known version to allow a fresh setup was 1.6.4.44~ubuntu16.04.1
Note that once set up the urrent version works fine.
(-I've no idea where unity-mail stores setup info, not in it's .conf file so needed another install of 16.04 to (re)see issue..

Terminal shows on 1st. run,
~$ unity-mail
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
Traceback (most recent call last):
  File "/usr/share/unity-mail/UnityMail/application.py", line 567, in on_dialog_response
    self.load_data_from_dicts()
  File "/usr/share/unity-mail/UnityMail/application.py", line 590, in load_data_from_dicts
    for strFolder in dct['Folders'].split('\t'):
KeyError: 'Folders'

Then just hangs until Cancel is clicked