If you send messages using a bulk mailing vendor or a third party affiliates, check out Gmail's Bulk Senders Guidelines, including: Publish an SPF record that includes the IPs of the vendor or affiliates which send your messages.
Sign your messages with a DKIM signature that is associated with your domain.
Make sure the domain in the "From:" address matches the domain you're using to authenticate your emails.
If you send messages using a bulk mailing vendor or a third party affiliates, check out Gmail's Bulk Senders Guidelines, including: Publish an SPF record that includes the IPs of the vendor or affiliates which send your messages. Sign your messages with a DKIM signature that is associated with your domain. Make sure the domain in the "From:" address matches the domain you're using to authenticate your emails.
https://support.google.com/mail/answer/81126