Here is the log from the console
(pantheon-mail:31085): GLib-WARNING **: g_set_application_name() called multiple times
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_get_allocated_height: assertion 'GTK_IS_WIDGET (widget)' failed
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_get_allocated_height: assertion 'GTK_IS_WIDGET (widget)' failed
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_get_allocated_height: assertion 'GTK_IS_WIDGET (widget)' failed
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_get_allocated_height: assertion 'GTK_IS_WIDGET (widget)' failed
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_get_allocated_height: assertion 'GTK_IS_WIDGET (widget)' failed
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_get_allocated_height: assertion 'GTK_IS_WIDGET (widget)' failed
(pantheon-mail:31085): Gtk-CRITICAL **: gtk_widget_set_visible: assertion 'GTK_IS_WIDGET (widget)' failed
** (pantheon-mail:31085): ERROR **: app-conversation-set.vala:122: Couldn't add duplicate email [388/null] to conversation [#5] (2 emails)
Trace/breakpoint trap (core dumped)
This looks like a duplicate of Bug #1645790