I hate that every email client also contains a poorly implemented database. Why is that part not standard and completely separate from the send/receive protocols and UI?

I've got pretty large mailboxes and have never had any problems. I used to be incredibly picky about mailreaders, but I've never had any complaints about Mail.app.

I have about 20k messages in my All Mail and around 5k in inbox, and it's pretty unwieldy. Usable, but definitely slow switching mailboxes, slow at searching, slow at sorting and filtering, slow to bring up message windows and so on. It's more UI lag than anything else.

It is a very fast mail client with near empty mailboxes.

I have mailboxes with over 70-100k messages in them in Mail.app, and they never take longer than about 0.5-2.5 seconds to load up when switching to them (the higher range being when the system is also under load).

I have a few small gripes with Mail.app (it occasionally claims that some messages are unread that aren't, for instance), but nothing I've seen of other mail clients has led me to think they'd ever be better for my workflow.

I've got about 80k messages total across two mail accounts, and it works fine. Scrolling through it takes time, but everything else is fine. Searching, filtering, sorting and switching mailboxes are not instantaneous, but reasonably fast. Certainly not unwieldy.

mail works fine for me with a large inbox (GMAIL).