Swift_TransportException: Expected response code 250 but got code "", with message "" in AbstractSmtpTransport.php:383

I have a laravel application that has been sending emails for Years now. Recently, emails have been failing to send. When I check the failed_jobs table, below is the error message:

Swift_TransportException: Expected response code 250 but got code "", with message "" in 
/apps/www/ccc.xxxx.com/public_html/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/AbstractSmtpTransport.php:383

Below are things I have attempted:

• composer dump-autoload
• php artisan config:cache
• php artisan config:clear
• php artisan queue:restart
• restarted supervisor
• Ensure username and password is correct in .env file
• I have connected to the mail box successfully and able to send email to anyone

Below is the .env config

MAIL_DRIVER=smtp
MAIL_HOST=smtp.office365.com
MAIL_PORT=587
MAIL_USERNAME=g.blah@balh.com
MAIL_PASSWORD=Va#@2016
MAIL_ENCRYPTION=TLS

What can be the issue and how to fix this ?

via Chebli Mohamed