Gmail - Label emails based on sender domain

labeler.gs

function main() {
    const labelMap = new Map();
    Gmail.Users.Labels.list("me").labels.forEach((label) => {
        if (label.type == "user") labelMap[label.name] = label.id;
    });
    if (messageList = Gmail.Users.Messages.list("me", {
            q: "in:Inbox has:nouserlabels",
        }).messages) {
        messageList.forEach((msg) => {
            const newLabel =
                "Sender/" +
                GmailApp.getMessageById(msg.id)
                .getFrom()
                .match(/\s*"?([^"]*)"?\s+<(.+)>/)[2]
                .replace(/.*@/, "")
                .replace(/\..*$/, "");
            if (newLabel in labelMap) {
                // label email
                Gmail.Users.Messages.modify({
                        addLabelIds: [labelMap[newLabel]]
                    },
                    "me",
                    msg.id
                );
            } else {
                // create label, add to map
                labelMap[newLabel] = Gmail.Users.Labels.create({
                        name: newLabel
                    },
                    "me"
                ).id;
                // label email
                Gmail.Users.Messages.modify({
                        addLabelIds: [labelMap[newLabel]]
                    },
                    "me",
                    msg.id
                );
            }
        });
    } else {
    console.log("no unlabelled mail")
    }
}