function main() {
    var campaigns = AdsApp.campaigns().get();
    var budgetLimit = YOUR_BUDGET_LIMIT; // Set your daily budget limit here
    var notificationThreshold = 0.9; // 90% of the budget limit
    var emailRecipient = 'YOUR_EMAIL_ADDRESS';

    while (campaigns.hasNext()) {
        var campaign = campaigns.next();
        var campaignName = campaign.getName();
        var stats = campaign.getStatsFor("TODAY");
        var cost = stats.getCost();
        var budgetProportion = cost / budgetLimit;

        if (budgetProportion >= notificationThreshold && budgetProportion < 1) {
            // Send an email notification if the budget is nearing its limit
            sendEmail(emailRecipient, 'Budget Alert for ' + campaignName, 
                      'The campaign "' + campaignName + '" is nearing its daily budget limit.');
        }

        if (budgetProportion >= 1) {
            // Proportionally adjust bids
            var adGroups = campaign.adGroups().get();
            while (adGroups.hasNext()) {
                var adGroup = adGroups.next();
                var currentBid = adGroup.bidding().getCpc();
                var adjustedBid = currentBid * (1 - budgetProportion); // Adjust the bid based on spend
                adGroup.bidding().setCpc(adjustedBid);
            }

            // Send an email notification about bid adjustment
            sendEmail(emailRecipient, 'Bid Adjustment for ' + campaignName, 
                      'The bids for campaign "' + campaignName + '" have been adjusted due to budget limit.');
        }
    }
}

function sendEmail(recipient, subject, body) {
    MailApp.sendEmail({
        to: recipient,
        subject: subject,
        body: body,
        name: 'YOUR_EMAIL_SENDER_NAME'
    });
}