If it's really a beta in the true sense of the word, it's not reliable enough to export one's mails. It would be better to wait till it's out of beta for those who need flexibility to move out.
Beta features are reserved for paying customers (and in this case you also have to apply to get the IMAP functionality). Free accounts don't get it until it becomes stable.
> The best way is to upgrade your account to a paid account and take advantage of the numerous extra features we provide with paid accounts. [0]
