Before you set up SPF
From: https://support.google.com/a/answer/10686639?hl=en&ref_topic=10685331&sjid=16475661690433716483-NC#zippy=%2Cget-the-sign-in-information-for-your-domain-provider 







Before you set up SPF
Protect against spoofing & phishing, and help prevent messages from being
marked as spam

Sender Policy Framework (SPF) is an industry-standard email authentication
method. It’s an effective way to help protect your domain from spoofing,
and to help prevent your messages from being marked as spam. So we recommend
you always set up SPF for your organization.
Tip: If you send email with Google Workspace only, get your SPF record in
Define your SPF record—Basic setup.

Note: If you bought your domain from a Google partner when you signed up for
Google Workspace, you might not need to set up SPF records. Check if SPF is
one of the Settings managed by your domain host.

Before you set up email authentication, use the Google Admin Toolbox to
check if SPF and DKIM have been set up.




We’re here to help
We’ve tried to simplify SPF setup, but some steps can be technical. Read
these articles thoroughly, and we’ll walk you through the process. We’re
confident you can successfully implement SPF.

If you haven’t yet, watch our email authentication videos. These videos
have helpful information about how to set up SPF and other email
authentication methods.




Take these steps before you set up SPF




Get the sign-in information for your 
domain provider

SPF is set up at your domain provider, not in your Google admin console.
You’ll need the sign-in information for your domain provider.
If you're not sure who your domain provider is, go to Identify your domain
host.






Understand IP addresses

An IP address is used to identify devices and connect to the internet. IP
addresses let devices like computers, mobile devices, and servers communicate
with each other. Servers that send and receive email are identified by their
unique IP address. The SPF record for your domain might need the IP addresses
for servers that send email for your domain.

IP address blocks
IP addresses are typically assigned to networks in blocks. An IP address
with a slash (/) indicates a block of IP addresses:

When you use an IP block address in your SPF record, the SPF record is
applied to all IP addresses in the block.






Understand DNS TXT records

To set up SPF for your domain, add a DNS text (TXT) record in your domain
provider's management console. TXT records are a type of DNS record that has
information for servers and other sources outside your domain.  Learn more 
about TXT records.






Check if you have an existing SPF record (optional)

You might already have a TXT record set up for SPF with your domain
provider. To check, use the Check MX feature in the Google Admin Toolbox:

  1. Go to the Google Admin Toolbox.

  2. Enter your domain name.

  3. Click Run Checks!

  4. When the test finishes, click Effective SPF Address Ranges.

  5. Check the SPF results. They should include:

    • .google.com

    • .google.com followed by several IP addresses

    • .google.com followed by several IP addresses

    • .google.com followed by several IP addresses





Identify all email senders for your organization
Your SPF record must include references to all servers that send email for your 
organization or domain. These might include:

If you send email with servers or services in addition to Google Workspace, 
gather those IP addresses or domains to include in your SPF record. You might 
need to contact your web site admin or third-party service documentation for 
this information.




Next steps
Now that you're prepared to set up SPF, define your SPF record: