GSuite, by default, sends all outgoing emails through its own servers. However, you can configure G Suite to allow individual users, who are sending from other domain names (i.e. outside your GSuite hosted domains), to be allowed to specify an SMTP server for those outgoing emails.
The first step is to allow per-user outbound gateways as per the instructions given here.
Then, individual users can add their own email address following these instructions.
The SMTP server to enter is mail.smtp2go.com. Enter your SMTP2GO username into Username and your SMTP2GO password into Password.
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