Hi, to use our Email SMTP service with Gmail accounts first do the following in managing their account:

1) Security >> Less secure app access >> Turn on
2) Security >> Signing Into Google >> 2 Step Verification >> Turn on
3) After you've enabled 2 step verification, go to Security >> Signing Into Google >> App Passwords >> Create app password
4) Use app password as password linked to user email address in SMTP setting

Best Regards,
HansaWorld Support