back up emails from an account that will be closed by the provider

Dear All,

I have an email account whose provider is about to discontinue their service. I want to back up the mailbox so that I can retrieve messages at a later date. A couple of questions:

Can I archive the mailbox for later retrieval? Or should I be backing up the mailbox as an mbox file? In either case, will I be able to retrieve those files for reading?

Your thoughts gratefully received. Thank you in advance,

C