save my mails to personal storage

Question

hello experts

 

hope i am asking at the right place.

 

I use an MBP High Sierra. my outlook is configured with my gmail account through IMAP. my inbox will be full in next few weeks. i am seeking the best suggestion to move them to my personal storage, just not for the sake of freeing space in my mail account but also to have a safe copy with myself.

thanks in advance