That's a misfeature:
- if you check it too often (like every 10 mins), you get bugged too many times (usually you hear a sound and some message near the system tray)
- if you check it too seldom (like, every 2-3 hours), you could find out about stuff too late; things could get worse if the email server is down exactly when you check it (happened to me a few times)
- the program should alert you only when emails that interest you arrive (see below)
However, alerting you when new messages arrive, that's a completely different matter (in other words, the mail reader can check and download new messages every minute if it wants to, but it can tell me about new messages every hour).
New email messages can be split into 2 categories:
- message from someone you already know, related to some matter you probably know
- message from someone you don't know yet (so you don't yet know how you should react)
In the latter case, new email will just go into the root folder, which is usually ok anyway.
Having that, here's what should happen:
- For certain folders, you can have an alert (when a message gets routed to a folder, play a sound).
- Otherwise, let the program alert you every hour or so (of new mail)
What is achievable now:
- there's an extension for Thunderbird: "Mailbox Alert" which can trigger an action when a new email arrives into a certain folder (the case 1 above)
- anyway, every hour or so, I read new mail (the case 2 above)