SPF Stands for Sender Policy Framework and acts as a list of all of the authorized IP addresses and hosts for a domain. This list is published in the DNS records for each domain. The purpose of an SPF record is to prevent spammers from sending messages with forged From addresses at your domain.
In combination with DMARC or Domain-based Message Authentication, Reporting and Conformance, SPF protects against spam and phishing emails by checking the credentials of an email against the receiving mail server during delivery.
DKIM stands for DomainKeys Identified Mail and is used as a form of digital signature for emails. You can commonly see this as "signed by" in the details of an email. DKIM takes a public key from a domain and embeds a cryptographic checksum into an email. It then compares the two to verify that the contents have not been tampered with at any point.
SPF and DKIM are both used when setting up the Remove Branding add-on. Learn more about how to remove the tawk.to branding and replace it with your own in this article: Setting up the Remove Branding add-on