Case study: making a huge IMAP account work again with Mail.app

Problem

A 40 Gb Gmail account, accessed via IMAP with Mail.app. The machine has it harder and harder to still work. Old mails do not need to be instantly accessible.

Solution

Assign old mail a historic label (you can use a filter like before:2010/01/01). Activate Advanced IMAP feature lab in Gmail. In the Label tab, uncheck visible in IMAP for the historic label. The machine works again, the new mails are instantly available and for the old ones, web interface at the rescue!

Notes

Mail.app is notorious for not allowing IMAP unsubscription (except on Exchange). Fortunately, IMAP subscription is a server-side feature. So, if enabled at Gmail-level, all mail clients will comply. Even stoopid Mail.app.

I still have to check how Mail.app behaves with an already cached folder. Does it empty the cache accordingly (this is what is expected)?