gyb
Command line tool for locally backing up Gmail messages using Gmail's API over HTTPS.
TLDR
Estimate the number and the size of all emails on your Gmail account
$ gyb --email [email@gmail.com] --action estimate
Backup a Gmail account to a specific directory
$ gyb --email [email@gmail.com] --action backup --local-folder [path/to/directory]
Backup only important or starred emails from a Gmail account to the default local folder
$ gyb --email [email@gmail.com] --search "[is:important OR is:starred]"
Restore from a local folder to a Gmail account
$ gyb --email [email@gmail.com] --action restore --local-folder [path/to/directory]