Domain setting

Add SPF record

https://support.google.com/a/answer/33786?hl=en#zippy=%2Ctxt-record-for-spf%2Cadd-a-new-mail-server-or-domain-to-your-spf-records

Add TX record to your DNS
IP address is from servers which will send your emails

Example:
v=spf1 ip4:192.168.0.1/16 include:_spf.google.com include:sparkpostmail.com ~all

v=spf1 include:_spf.google.com ip4:185.2.168.81/32 ip4:150.136.20.28 -all

Create DMARK record

Add TXT record

v=DMARC1; p=reject; rua=mailto:postm@dmseomarketing.com, mailto:dmarc@dmseomarketing.com; pct=100; adkim=s; aspf=s

https://support.google.com/a/answer/2466563?hl=en