Sample run after shutting down evolution.  I created on new calendar event, viewed another, and then clicked on the Mail button.   Within 5 seconds the popups appear.   Never connected to imap server. 

# evolution -c calendar --offline 

(evolution:3265): Gtk-WARNING **: No object called: combobox-category

(evolution:3265): libebook-WARNING **: e-book.c:3095: cannot get book from factory: Invalid source

(evolution:3265): e-data-server-ui-WARNING **: ENameSelector: Could not load "Ubuntu One": Invalid source

(evolution:3265): GLib-GObject-CRITICAL **: Object class EMFolderTree doesn't implement property 'paste-target-list' from interface 'ESelectable'

(evolution:3265): GLib-GObject-CRITICAL **: Object class EMFolderTree doesn't implement property 'copy-target-list' from interface 'ESelectable'

(evolution:3265): calendar-gui-WARNING **: e-task-table.c:1589: Could not get the objects
(evolution:3265): libecal-DEBUG: e-cal.c:452: ECal GDBus connection is closed, remote peer vanished

(evolution:3265): libecal-WARNING **: gdbus_cal_disconnect: Failed to close calendar, GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.evolution.dataserver.calendar.Cal' on object at path /org/gnome/evolution/dataserver/calendar/3241/1

(evolution:3265): libecal-DEBUG: e-cal.c:452: ECal GDBus connection is closed, remote peer vanished

(evolution:3265): libecal-WARNING **: gdbus_cal_disconnect: Failed to close calendar, GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.evolution.dataserver.calendar.Cal' on object at path /org/gnome/evolution/dataserver/calendar/3241/2

(evolution:3265): libecal-DEBUG: e-cal.c:452: ECal GDBus connection is closed, remote peer vanished

(evolution:3265): libecal-WARNING **: gdbus_cal_disconnect: Failed to close calendar, GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.evolution.dataserver.calendar.Cal' on object at path /org/gnome/evolution/dataserver/calendar/3241/3

(evolution:3265): libecal-DEBUG: e-cal.c:452: ECal GDBus connection is closed, remote peer vanished

(evolution:3265): libecal-WARNING **: gdbus_cal_disconnect: Failed to close calendar, GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.evolution.dataserver.calendar.Cal' on object at path /org/gnome/evolution/dataserver/calendar/3241/4

(evolution:3265): libecal-DEBUG: e-cal.c:452: ECal GDBus connection is closed, remote peer vanished

(evolution:3265): libecal-WARNING **: gdbus_cal_disconnect: Failed to close calendar, GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.evolution.dataserver.calendar.Cal' on object at path /org/gnome/evolution/dataserver/calendar/3241/5

(evolution:3265): libecal-DEBUG: e-cal.c:452: ECal GDBus connection is closed, remote peer vanished

(evolution:3265): libecal-WARNING **: gdbus_cal_disconnect: Failed to close calendar, GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface `org.gnome.evolution.dataserver.calendar.Cal' on object at path /org/gnome/evolution/dataserver/calendar/3241/6

(evolution:3265): libecal-DEBUG: GDBus connection is closed, remote peer vanished