...

2. logout, log back in immediatly, there is no re-indexing and the list is available in < 1 second.
3. logout, log back in 12 minutes later. The list is returned in apx 15 seconds and again in a lsof I see pop3 accessing files inside the cur/ directory. ...

Of added note, when running a stat on the index files (dovecot.index, dovecot.index.cache, dovecot.index.log), the Modify and Change parameters remain static (no changes). So if it's rebuilding anything it's doing it in memory and not modifying the index files.

If I deliver a new message to the account, it does rebuild the files for sure and increments the Modify and Change params.

Perhaps what you might be seeing is file system caching. I notice this when performing NFS I/O tests: the first re-read is fast but decays over time as data is rolled out of the cache.

Joseph Tam tam@math.ubc.ca