Every so often outlook pops up a message that asks if you want to archive your email. It compresses the data file if you say yes. You can also set it to autoarchive (compresses them automatically).
Fall back plan is you email each of the people you have been swapping important email with and ask if they have copies. We do this all the time at work. It's so common no one even laughs when you ask. (If you are too embarased say the server crashed.)