30 as a normal family is interesting? I think most people wouldn’t consider that normal unless you’re dipping deep into cousins. However, your point is valid though that 30 does not qualify for scalability.
That said, the webUI doesn’t lag at all for me and I have no errors or warnings in the console. No one who uses it has reported those things to me either. Are you sure you set everything up properly? I did have performance problems back when I did still have errors and warnings in my console. If your cron tasks are setup properly everything should be smooth.
To be fair, I don’t have any experience with the webmail though.