Once you sign up your domain for G Suite, you will have to change its MX records to start using their email services.
You will need to assign the following MX records for your domain (make sure that you remove any previous MX records):
Priority Mail Server
1 ASPMX.L.GOOGLE.COM
5 ALT1.ASPMX.L.GOOGLE.COM
5 ALT2.ASPMX.L.GOOGLE.COM
10 ALT3.ASPMX.L.GOOGLE.COM
10 ALT4.ASPMX.L.GOOGLE.COMThe above instructions are in full compliance with the official G Suite instructions. They will require up to 72 hours to propagate and take effect. After that, your mail will be handled exclusively by G Suite.