I have 6 email accounts receiving about 3-500 messages per week. This is how I manage (using Gmail):
- I unsubscribe from mail I don't want to receive & customise my email notification settings for all online services (Trello, Facebook, Yammer, Github, etc.)
- Forward all incoming mail from all accounts to one primary account (in Gmail go to Settings -> Forwarding and add a forwarding address)
- On the primary account, I have my 'send mail as' addresses configured so I can appear to be sending mail from any of my addresses, all from within my primary account (Settings -> Accounts -> Send mail as). Note I also have 'reply from the same address to which the message was sent' setting checked.
- My primary account uses priority inbox: on the Settings -> Inbox page, set "Inbox type" to "priority inbox", with 3 sections: 1. Unread, 2. Starred, 3. Everything else
- When new mail comes in, I read it ASAP and if it requires some action, star it.
- Every morning I spend about half an hour going through the starred mail, do whatever action is required for each one, and unstar the message. I like to get it down to at most 10 starred messages waiting to be actioned. Then once every week or two I get this down to zero.
- Filing systems are needlessly oppressive and dehumanising. Don't waste your precious intelligence on sorting and retrieving things, that's what computers are for!
- Just because the message was delivered in internet time, doesn't mean you have to reply immediately. I often take 2 weeks to reply to something, and just apolgise nicely for the delay. No stress.
- It might pay to turn off your spam filter on your secondary accounts, because you'll never think too check the spam folder for an account you never look at