Gmail Offline backup

I always felt the need to keep my Gmail account emails in my PC as an offline local backup just in case that for any reason I'm unable to log into my account. The two means that I explored so far are:

1) Use Microsoft Office Outlook to synch and download my Gmail account. My concern regarding this approach is if the download process is secure, i.e., encrypted end to end?

2) Gmail offers within your account the option of downloading your email messages complete with any attachments. My question again: is that download secure? And also, Gmail uses a special extension format for this downloaded file. Can that file be opened in any Email client? (Outlook, Thunderbird, etc)

Thanks