* SPF: Tell the world which servers are allowed to send email for your domain
* DKIM: Weak version of digitally signed email, add a header that only mailservers that have the private key you supply can generate. Tampering invalidates the signature (for example when an email gets relayed for a second time). The private key used counts for your whole domain.
* DMARC: Tells other mailservers what to do when the SPF and/or DKIM check fails, and also allows you to set an address where to send reports to. These reports contain counts of messages that failed the SPF and/or DKIM checks.
* SPF: Tell the world which servers are allowed to send email for your domain
* DKIM: Weak version of digitally signed email, add a header that only mailservers that have the private key you supply can generate. Tampering invalidates the signature (for example when an email gets relayed for a second time). The private key used counts for your whole domain.
* DMARC: Tells other mailservers what to do when the SPF and/or DKIM check fails, and also allows you to set an address where to send reports to. These reports contain counts of messages that failed the SPF and/or DKIM checks.