Webmail is comically slow and laggy even if it permanently stores every single email in the database. It also doesn't prune them after deletion and that's a huge privacy issue imho. The fact that it's saving all the emails in clear on the database Is concerning for use outside self hosting. Even if it could be set to do end to end encryption for files, in this way the admin has full access to all emails from all users (well, actually, thanks to the impersonation plugin it has access to everything and it doesn't even give a "admin has logged in" notification).
Also, even if it's this slow, it's incredibly barebone.
I replaced it with snappymail which is way faster even if it doesn't cache any email in the database
I tried many webmail software and I didn't see any of them storing emails on the database. Afterlogic, roundcube, squirrel, they're all reading them from IMAP with no DB. But they're much faster. What's the point of storing millions of emails on a DB if the software is 50x slower than something that doesn't do that?