Sylpheed-Claws isn’t especially heavy on RAM, but something that can feel strange is that when switching from a big folder to an empty one, the RAM usage doesn’t go down. This is because the GtkCTree widget uses GMemChunks to allocate memory, and this thing doesn’t free it when not needed anymore; rather, the glib reuses them. OK. But I thought it’d be nice to force cleaning of stuff from time to time. From the documentation, I can read:

void g_mem_chunk_clean (GMemChunk *mem_chunk);

Frees any blocks in a GMemChunk which are no longer being used.

Let's try!

...

Hmm, it does nothing visible. Let's see...

From glib/gmem.c:

void        g_mem_chunk_clean       (GMemChunk *mem_chunk)  {}

Notice the empty function body.