zlacker

SPF is trivial to set up for people who already have their own domain; it's literally 1 DNS TXT record.

I'm not aware of any mail providers that require DNSSEC. Were you thinking of DKIM? That's just 1 more TXT record (to publish the public key used to verify the signature), and some mail signing software if your mail server doesn't have that feature built-in (which is freely available).