SPF & DKIM
The SPF record is a line that you can add to your DNS server to prevent impersonation of your mail servers.
Receiving servers examine the SPF record to ensure and verify that the server responsible for sending the emails has been authorised to do so by the sending domain.
This reduces the risk of your domain being used for SPAM.
https://fr.wikipedia.org/wiki/Sender_Policy_Framework
The DKIM standard :
Anti-spam policies are becoming increasingly strict. To ensure that your emails are sent smoothly and that your recipients receive them without security tools blocking them, you need to set up parameters to authenticate your messages and validate their content. The aim of the DKIM protocol is not just to prove that the domain name has not been usurped, but also that the message has not been altered during transmission. This protocol is based on a cryptographic procedure, with a public key published in the DNS zone of the sending domain, and a private key used to encode the message. The private key is used to add a signature to the header (where all the characteristics of the message are stored) of each message sent. Usually the key comes from the mail server.