What is this? "v=spf1 ip4:000.000.000.000 a mx ~all"
Where 000.000.000.000 is my servers IP. What is this for IP6? "v=spf1 ip4:000.000.000.000 a mx ~all"
This is an SPF DNS TXT record saying that the IP in the domain's A record, MX record and the IP 000.000.000.000 are permitted to send email for that domain, and that messages from all other servers should be soft-rejected (~all instead of -all). For IPv6, it would be, for example, ip6:ABCD::1234/128 to allow messages from ABDC::1234. You can see the SPF record syntax reference for more information.