figure - nonblocking progress indicatorview gui itself--the gui responds to movesredrawsand resizes during the transfers other transfers such as mail deletes must run all by themselves and disable other transfers until they are finisheddeletes update the inbox and internal caches too radically to support other parallel operations on systems without threadspymailgui instead goes into blocked state during such long-running operations (it essentially stubs out the thread-spawn operation to perform simple function callbecause the gui is essentially dead without threadscovering and uncovering the gui during mail load on such platforms will erase or otherwise distort its contents threads are enabled by default on most platforms that run python (including windows)so you probably won' see such oddness on your machine the pymailgui client