[Enhancement] Automatic or manual pruning

[Kabouik]

Pruning cache to a maximal size set in main.conf would be useful for accounts with large inbox, as well as devices with limited storage (SBCs, phones, servers).

Not sure what criteria would be relevant for pruning. Date/age of messages, list of white-listed folders? Should a prompt be shown when the maximal set size is reached or should oldest emails be removed from cache quietly?

Pruning cache/ and temp/ separately would be great for accounts with encryption enabled, but you reported that there is no free solution to partially decrypt sqlite. Just mentioning it here for future reference, since this would allow the advantages of full cache (offline use, speed, search index in all folders) without the extra disk space of full folder decrypting in /temp.