I use i3 wm and want to have a notification for new emails in i3 status line.

You need to have a fresh version of rust and cargo

Clone this repository and build release version

git clone https://github.com/Crandel/rust_gmail_checker.git

cd rust_gmail_checker

cargo build --release

After building you could move the binary file inside your PATH

mv target/release/rust_gmail  ~/.local/bin/rust_gmail

During first run it will fail and create .email.json file with this structure

[
    {
        "mail_type": "gmail",
        "account": "account_name",
        "short_conky":"A",
        "email": "<username>@gmail.com",
        "password": "<password>"
    }
]

Just edit this file and you will get this result

$ rust_gmail
A:0

You could use several gmail accounts to have a personal and work notifications