Tune the Header Cache

Prerequisites

1. NeoMutt built with a header cache backend.

2. A working cache directory on local storage.

Choose a Cache Location

1. Pick a directory for caches:

set header_cache = "~/.cache/neomutt/hcache"
set message_cache_dir = "~/.cache/neomutt/bcache"

2. Restart NeoMutt.

Expected result: NeoMutt creates cache files in the selected locations.

Select a Backend Explicitly

1. If multiple backends are available, pin one:

set header_cache_backend = "lmdb"

Expected result: NeoMutt uses the specified backend for header cache storage.

Enable Cache Compression

1. Turn on compression to reduce disk usage:

set header_cache_compress_method = "zstd"
set header_cache_compress_level = 3

Expected result: cache files shrink at the cost of extra CPU.

Keep the Cache Clean

1. For body caches, enable cleaning only when needed:

set message_cache_clean = yes

2. Disable it again if you notice performance impact.

Expected result: cache files no longer reference messages removed by other clients.

See How to Set Up Header/Body Caching for full details and supported backends.