An SPF record is a TXT record in the domain DNS that lists the mail servers that are allowed to send email from your domain. In some instances virus guards and spam filters may mistake messages hasn’t got the SPF record as spam.
For GSuite goto Google support: https://support.google.com/a/answer/33786
Sign in to your domain account at your domain host.
Locate the section for updating your domain’s DNS records. This may be called DNS management, or DNS advanced settings.
Add a TXT record:
- Name/Host/Alias: Enter @ or leave it blank. Your other DNS records might indicate which entry is correct.
- Time to Live (TTL): Enter 3600 or leave the default.
- Value/Answer/Destination: Enter v=spf1 include:_spf.google.com ~all
If a TXT record already exists for SPF record, update it to the Google SPF: https://support.google.com/a/answer/33786#update_spf
To add a mail server’s domain, use an include statement for each domain including the Google domain.
- v=spf1 include:serverdomain.com include:_spf.google.com ~all
example: v=spf1 ip4:172.16.254.1 include:_spf.google.com ~all
Check Google MX toolbox for SPF and domain: https://toolbox.googleapps.com/apps/checkmx/