callback function not working in node-scheduler

I have successfully written a code to read unseen emails in my email box using node.js. it works fine when I run it in the normal javascript file. now I want to schedule the script to run every 30 seconds. so wrote a code snippet using node-scheduler as below. running this I just get reading unread emails....### as output, console.log(msg); not print anything. if I run this without nod-scheduler it works fine. what might be the problem? I tried await keyword with email.unreadEmail function, it didn't work too.

I believe that this is something happening because of asynchronous behavior. if so is there way to convert this code to promises? I am little bit confiuse because there are multiple nexted callback in imap interface.

schedule.scheduleJob('*/30 * * * * *', () => {

    logger.info(`scheduler runs at ${new Date()} for check unread emails`);
    let email = new mail.default();
    email.unreadEmail((msg) => {
        console.log(msg);
    });

});

here is the code for email reading

unreadEmail(callback){

        logger.info(`reading unread emails....###`);

       imap.once('ready', () => {

            openIncidents((err, box) => {
                if (err) throw err;
                imap.search([ 'UNSEEN'], (err, results) => {
                    if (err) throw err;

                    try{
                        // var f = imap.fetch(results, { bodies: '',markSeen: true });
                        var f = imap.fetch(results, { bodies: '' });
                        f.on('message', (msg, seqno) => {
                            console.log('Message #%d', seqno);
                            var prefix = '(#' + seqno + ') ';
                            msg.on('body', (stream, info) => {

                                simpleParser(stream, (err, mail) => {

                                    callback(mail.subject);

                                });

                                // stream.pipe(fs.createWriteStream('msg-' + seqno + '-body.txt'));
                            });
                            msg.once('attributes', function(attrs) {
                                logger.info(prefix + 'Attributes: %s', inspect(attrs, false, 8));
                            });
                            msg.once('end', function() {
                                logger.info(prefix + 'Finished');
                            });
                        });
                        f.once('error', function(err) {
                            logger.error('Fetch error: ' + err);
                        });
                        f.once('end', function() {
                            logger.info('Done fetching all messages!');
                            imap.end();
                        });
                    }catch (e) {
                        logger.error('Error from fetching mails, probably there are no unseen emails in mailbox');
                    }

                });
            });
        });

        logger.info(`end of the email function....###`);

    }

Updated

this behavior is same with setInterval function

setInterval(()=>{
email.unreadEmail((msg)=>{...})}, 30000)

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