Reducing the annoying spams

Background:I have been working in the same company for more than 8 years, and I am the local department head with a team of around 15 people maximum. The team members come and go, and obsolete email addresses are forwarded to me, and therefore, my mail box is always flooded by spam. To worsen the situation, I'm the recipient of the popular alias like "info", "hostmaster" and "support".

I receive 100+ spam each hour on average, and after a typical weekend, my mail box will be flooded with over 5000 spam messages. And that is a result after moderate spam filtering, I mean using those less than aggressive filtering software so that I won't miss real email.

Solutions:

1. Hey, there's no possible real solution. All you can do is to reduce the trouble, recenly, I managed to reduce my inbox from ~1500 to less than 50 after a single night. So that's nice enough, right?
2. Forwarding your email to gmail: this could be a real elegant solution, the spam filtering from Google is doing a very great job. Usually only around 30 out of 1500 were left after their smart filtering algorithm. However, I won't recommend it as the first solution since it might not be very good for you to use a gmail account instead of your corporate email account. The company policy might also prohibits you to do this. However, this could be a real good backup in case your own spam filter wrongly kick some of your valuable real email as spam. This is always nice to have two sets of filtering algorithm working in parallel, and it increases the chance that the real emails can pass through.
3. Emails from ex-colleagues: We can filter inside thunderbird (or whatever email client you use) by the receipient and put them into separate folders. In most cases, those email addresses should not be receiving useful email any more, so a vast proportion of email from those email addresses were spam. So, you don't have to keep looking at them daily, you can scan through the title/sender around once or twice a week and that's enough. Similar, email from "info", "hostmaster" and any popular email aliases can be treated like this. But you better divide them into seperate folders.
4. Mailing list: if you're developers of any open source projects, these mailing list could be a major source of email. They're not spam, but they feel like spam when you don't need them. So, setup filters to put them into different folders accordingly. After that, treat them like newsgroups, i.e. you go there to read and reply only when needed.
5. Date filter: most real people will have the computer set correctly, so you can filter email older than around one years ago, as well as to send those later than next month directly to the trash folder safely.

Simple techniques work out the best, at least you will have a very clean inbox to begin your day if you do the above. Of course, some of the techniques there is just to push the problem forward, i.e. to let to scan through the pile of trash once or twice a week, but then it feels much better for you don't have to be forced to clean up the trash everyday.