How do i access all email? - nu7hatch/gmail GitHub Wiki
First review labels:
gmail.labels.all =>
["travel", "[Gmail]/All Mail", "[Gmail]/Drafts", "[Gmail]/Important",
"[Gmail]/Sent Mail", "[Gmail]/Spam", "[Gmail]/Starred", "[Gmail]/Trash"]
From the issues I think these are language dependent so, if you're in France it's not likely to be "[Gmail]/All Mail"
Second - access all mail via label
gmail.mailbox("[Gmail]/All Mail").count