Release memory after high load

[ngocnha]

The stalwart-email process starts with a memory usage of around 98 MiB. After copying 100 emails from my local folder to my email inbox folder, its memory consumption increases to 260 MiB and doesn't release the additional memory.
It doesn't stop there; it increases a little bit after a while.

[mdecimus]

Stalwart has a few internal caches. It could be that when you first started the app these caches were empty and now have data. What is important is that the memory usage does not keep increasing after that.