Keeping email records when moving between posts
You can use a permanent account while still having the emails sent to your official address.  I do this by getting gmail to check my university email accounts for me (Settings > Accounts > Check email from other accounts).  I am then able to reply to those emails directly in gmail, while having them appear to come from my university address (there is an option to always reply from the same address to which the email was sent).

I'm not sure whether this solution can be any use for the emails you have already received (you may be able to use it, if you can for example mark all your emails as unread, so that gmail maybe sees them as new), but it might be worth starting now to reduce future hassle.