If you ever tried to send emails from your Office365 account directly from Gmail , you might have experienced an issue that prevents you from authenticating. Yes, you have carefully followed all the instructions and your credentials are correct, but you are still getting this error message: Authentication failed: Please check your username/password Don't worry, you are not alone! The problem is that the default SMTP server ( smtp.office365.com ) is not always successfully translated into the correct IP address. In order to make it work, just follow these instructions: 1) Open your command line or terminal 2) Type ping smtp.office365.com 3) You will see that a different domain name is displayed. In my region (Europe) it is outlook-emeawest.office365.com 4) Use that domain when you enter your Office365 SMTP server details on Gmail