I have tried Google G suite in the past and it is quite a few settings that need to be done in order to make SMTP to work using G Suite. I can't remember by hart what have to be done but one is for sure that you have to setup correct DNS records...., here is the link where you can find some useful tips:

https://support.google.com/a/answer/33353?hl=en&ref_topic=4445319&authuser=2