Setting up the proper SPF records for you domain will improve the deliverability of your emails.

Official Google Documentation

https://support.google.com/a/answer/2466563

Quick Setup

Add this TXT record to your DNS settings:

Type: TXT

Name: @

Content: v=spf1 include:_spf.google.com ~all

Example

Verify Setup

Use this tool to test your domain setup: https://toolbox.googleapps.com/apps/checkmx/

You should see this SPF setting:

If properly setup you will see it turn green: