We are always talking to clients about ways to "get stuff out of your head and into a trusted system" and we have found that Evernote is often a great place to start and can be a key component of the trusted system for many people.
Here is a quick tip video showing how to easily get important email saved into Evernote.
Pro tip here... if you add @notebook name or #tag name to the end of the title of the forwarded email, you can have the note "auto file" itself in your system.
For example if you have a notebook called travel and you use tags like receipt and reservation, your forward email subject line might look like this...
FWD: Hotel reservation & confirmation for London Trip @travel #receipt #reservation
For more pro tips on emailing to evernote, check out their support article here