Did you know that Google Compute engine does not allow outbound connections on port 25, 465 and 587?
By default design, these SMTP ports are not listening by as they are susceptible to a large amount of abuse. Even though standard email ports are blocked, you can choose a non-standard port to send email through.
While sending email from blocked ports is not allowed, your instances can still receive email but remember Port 25 is always blocked and cannot be used, even through SMTP relay using G-Suite.
Sending Emails with WordPress
Choose a third party Email Service and learn how to send emails from your WordPress Server.